Magnetic recording medium having controlled dimensional variation

ABSTRACT

In a magnetic recording medium, an average thickness tT is tT≤5.5 μm, a dimensional variation Δw in a width direction to tension change in a longitudinal direction is 650 ppm/N≤Δw, and a rate of shrinkage in the longitudinal direction is 0.08% or less.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/455,132, filed on Jun. 27, 2019, which application claims the benefitof Japanese Priority Patent Application JP 2019-067931 filed on Mar. 29,2019, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present technology relates to a magnetic recording medium.

BACKGROUND ART

In recent years, in magnetic tapes (magnetic recording media) used forcomputer data storage, the track width and the distance between adjacenttracks are greatly reduced for improving data recording density. Thusreduction of the track width and the distance between tracks furtherdecreases the maximum acceptable variation as dimensional variation ofthe tape itself caused by environmental factors such as temperature andhumidity change.

Some technologies for reducing dimensional variations have beenproposed. For example, in the magnetic tape medium disclosed in PatentLiterature 1, X×Y is 6×10⁵ or more and Y/Z is 6.0 or less when X is 850kg/mm² or more or less than 850 kg/mm², in which X is the Young'smodulus of a non-magnetic support in the width direction, Y is theYoung's modulus of the back layer, and Z is the Young's modulus of thelayer including a magnetic layer in the width direction.

CITATION LIST Patent Literature

[PTL 1]

JP 2005-332510A

SUMMARY Technical Problem

It is desirable to provide a magnetic recording medium which suppressesdimensional change in the width direction by adjusting the tensionapplied to the tape in the longitudinal direction.

Solution to Problem

In a magnetic recording medium according to an embodiment of the presenttechnology, an average thickness t_(T) is t_(T)≤5.5 μm,

a dimensional variation Δw in a width direction to tension change in alongitudinal direction is 650 ppm/N≤Δw, and

a rate of shrinkage in the longitudinal direction is 0.08% or less.

In the magnetic recording medium, a squareness ratio in a verticaldirection may be 65% or more.

The dimensional variation Δw may be 700 ppm/N≤Δw.

The dimensional variation Δw may be 750 ppm/N≤Δw.

The dimensional variation Δw may be 800 ppm/N≤Δw.

The rate of shrinkage may be 0.07% or less.

The magnetic recording medium includes a back layer, and a surfaceroughness R_(ab) of the back layer may be 3.0 nm≤R_(ab)≤7.5 nm.

The magnetic recording medium includes a magnetic layer and a backlayer, and a coefficient of friction μ between a surface on a side ofthe magnetic layer and a surface on a side of the back layer may be0.20≤μ≤0.80.

A 1% elongation load of the magnetic recording medium in thelongitudinal direction may be 0.60 N or less.

A thermal expansion coefficient α of the magnetic recording medium maybe 5.5 ppm/° C.≤α≤9 ppm/° C., and a humidity expansion coefficient β ofthe magnetic recording medium may be β≤5.5 ppm/% RH.

A Poisson's ratio ρ of the magnetic recording medium may be 0.25≤ρ.

An elastic limit value σ_(MD) of the magnetic recording medium in thelongitudinal direction may be 0.7N≤σ_(MD).

The elastic limit value σ_(MD) may not depend on a velocity V inmeasurement of elastic limit.

The magnetic recording medium includes a magnetic layer, and themagnetic layer may be vertically oriented.

The magnetic recording medium includes a back layer, and an averagethickness t_(b) of the back layer may be t_(b)≤0.6 μm.

According to one embodiment of the present technology, the magneticrecording medium includes a magnetic layer, and the magnetic layer maybe a sputtering layer.

In a case where the magnetic layer is a sputtering layer, an averagethickness t_(m) of the magnetic layer may be 9 nm≤t_(m)≤90 nm.

According to another embodiment of the present technology, the magneticrecording medium includes a magnetic layer, and the magnetic layer mayinclude a magnetic powder.

In a case where the magnetic layer includes a magnetic powder, theaverage thickness t_(m) of the magnetic layer may be 35 nm≤t_(m)≤90 nm.

The magnetic powder may include an ε-iron oxide magnetic powder, abarium ferrite magnetic powder, a cobalt ferrite magnetic powder, or astrontium ferrite magnetic powder.

In the magnetic recording medium, the squareness ratio in the verticaldirection may be 65% or more, and, the rate of shrinkage may be 0.07% orless.

In the magnetic recording medium, the squareness ratio in the verticaldirection may be 65% or more, and the magnetic recording medium includesa back layer, and the surface roughness R_(ab) of the back layer may be3.0 nm≤R_(ab)≤7.5 nm.

In the magnetic recording medium, the squareness ratio in the verticaldirection may be 65% or more, and the magnetic recording medium includesa magnetic layer and a back layer, and a coefficient of friction μbetween a surface on a side of the magnetic layer and a surface on aside of the back layer may be 0.20≤μ≤0.80.

In the magnetic recording medium, the squareness ratio in the verticaldirection may be 65% or more, and the 1% elongation load in thelongitudinal direction may be 0.60 N or less.

In the magnetic recording medium, the squareness ratio in the verticaldirection may be 65% or more, the thermal expansion coefficient α may be5.5 ppm/° C.≤α≤9 ppm/° C., and the humidity expansion coefficient β maybe β≤5.5 ppm/% RH.

In the magnetic recording medium, the squareness ratio in the verticaldirection may be 65% or more, and the Poisson's ratio ρ may be 0.25≤ρ.

In the magnetic recording medium, the squareness ratio in the verticaldirection may be 65% or more, and the elastic limit value σ_(MD) in thelongitudinal direction may be 0.7 N≤σ_(MD).

The elastic limit value σ_(MD) may not depend on the velocity V inmeasurement of elastic limit.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view depicting a configuration of a magneticrecording medium according to a first embodiment.

FIG. 2 is a cross sectional view depicting a configuration of magneticparticles.

FIG. 3A is a perspective view depicting a configuration of a measuringapparatus.

FIG. 3B is a schematic view depicting a detail of a measuring apparatus.

FIG. 4 is a graph depicting an example of an SFD curve.

FIG. 5 is a schematic diagram depicting a configuration of a recordingand reproducing apparatus.

FIG. 6 is a cross sectional view depicting a configuration of magneticparticles according to a modification.

FIG. 7 is a cross sectional view depicting a configuration of a magneticrecording medium according to a modification.

FIG. 8 is a cross sectional view depicting a configuration of a magneticrecording medium according to a second embodiment.

FIG. 9 is a schematic diagram depicting a configuration of a sputteringapparatus.

FIG. 10 is a cross sectional view depicting a configuration of amagnetic recording medium according to a third embodiment.

DESCRIPTION OF EMBODIMENTS

Favorable embodiments for performing the present technology aredescribed below. Note that the embodiments described below representtypical embodiments of the present technology, and the scope of thepresent technology will not be limited only to these embodiments.

The present technology is described in the following order.

1. Description of the present technology

2. First embodiment (example of magnetic recording medium of coatingtype)

(1) Configuration of magnetic recording medium

(2) Description of each layer

(3) Physical properties and structure

(4) Method for producing magnetic recording medium

(5) Recording and reproducing apparatus

(6) Effect

(7) Modification

3. Second embodiment (example of magnetic recording medium of vacuumthin film type)

(1) Configuration of magnetic recording medium

(2) Description of each layer

(3) Physical properties and structure

(4) Configuration of a sputtering apparatus

(5) Method for producing magnetic recording medium

(6) Effect

(7) Modification

4. Third embodiment (example of magnetic recording medium of vacuum thinfilm type)

5. Example

1. DESCRIPTION OF THE PRESENT TECHNOLOGY

There is a need to further increase the recording capacity of magneticrecording media (for example, magnetic recording tapes). For example, inorder to increase the recording capacity (recording area), furtherthinning of a magnetic recording medium (reduction of the totalthickness) for increasing the tape length per one cartridge productincluding a magnetic recording medium is suggested.

However, further thinning of a magnetic recording medium tends to causedimensional change in the track width direction. The dimensional changetends to occur particularly during long-term storage. Dimensional changein the width direction can cause undesirable phenomena for magneticrecording, such as an off-track phenomenon. The off-track phenomenonmeans the absence of the target track at the track position to be readby a magnetic head, or reading of a wrong track position by a magnetichead.

In the past, in order to suppress dimensional change of magneticrecording media, for example, a technology of adding a layer forsuppressing dimensional change of a magnetic recording medium was used.

However, addition of the layer may increase the thickness of themagnetic recording tape, and will not increase the tape length per onecartridge product.

The inventors are studying a long magnetic recording medium suitable foruse in a recording and reproducing apparatus which keeps the width ofthe magnetic recording medium constant or generally constant byadjusting the tension of the magnetic recording medium in thelongitudinal direction. The recording and reproducing apparatus detects,for example, the dimension or dimensional change of a magnetic recordingmedium in the width direction, and adjusts the tension in thelongitudinal direction on the basis of the detection result.

However, a magnetic recording medium with a suppressed dimensionalchange has a small dimensional variation in the width direction causedby tension change in the longitudinal direction. Therefore, it isdifficult to keep a fixed or almost fixed width of the magneticrecording medium even if tension adjustment in the longitudinaldirection is carried out with the recording and reproducing apparatus.

In consideration of the above circumstances, the inventors studied athin magnetic recording medium which is suitable for use in a recordingand reproducing apparatus which adjusts the tension in the longitudinaldirection, and suppresses the decrease of the suitability for the use inthe recording and reproducing apparatus caused by storage. As a resultof this, the inventors have found that a magnetic recording mediumhaving a specific configuration satisfies these requirements. Morespecifically, the present technology provides a magnetic recordingmedium having an average thickness t_(T) of t_(T)≤5.5 μm, and adimensional variation Δw in the width direction of 650 ppm/N≤Δw to thetension change in the longitudinal direction, and a rate of shrinkage inthe longitudinal direction of 0.08% or less.

The average thickness t_(T) of the magnetic recording medium accordingto the present technology may be 5.5 μm or less, more preferably 5.3 μmor less, and even more preferably 5.2 μm or less, 5.0 μm or less, or 4.6μm or less. The magnetic recording medium according to the presenttechnology is so thin that it allows, for example, the tape length woundin one magnetic recording cartridge to further increase, and thisincreases the recording capacity per one magnetic recording cartridge.

In the magnetic recording medium according to the present technology,the dimensional variation Δw in the width direction to the tensionchange in the longitudinal direction may be 650 ppm/N or more,preferably 670 ppm/N or more, more preferably 700 ppm/N or more, morepreferably 710 ppm/N or more, 730 ppm/N or more, 750 ppm/N or more, 780ppm/N or more, or 800 ppm/N or more. The dimensional variation Δw of themagnetic recording medium within the above-described value rangecontributes to allowing a fixed width of the magnetic recording mediumto be kept constant by adjusting the tension of the magnetic recordingmedium in the longitudinal direction.

The upper limit of the dimensional variation Δw is not particularlylimited, and may be, for example, 1700000 ppm/N or less, preferably20000 ppm/N or less, more preferably 8000 ppm/N or less, and even morepreferably 5000 ppm/N or less, 4000 ppm/N or less, 3000 ppm/N or less,or 2000 ppm/N or less. In a case where the dimensional variation Δw istoo great, stable traveling in the production process can be difficult.The method for measuring the dimensional variation Δw is described in2.(3).

In the magnetic recording medium according to the present technology,the rate of shrinkage in the longitudinal direction is 0.08% or less,and preferably 0.07% or less. If the rate of shrinkage is within theabove-described value range, suitability for the use in the recordingand reproducing apparatus will not change even after long-term storageof the magnetic recording medium. Therefore, undesirable phenomena formagnetic recording, such as an off-track phenomenon, hardly occur. Therate of shrinkage in the longitudinal direction may be, for example, 0%or more.

The method for measuring the rate of shrinkage is described in 2.(3)below.

The magnetic recording medium according to the present technologypreferably includes a back layer, and the surface roughness R_(ab) ofthe back layer is preferably 3.0 nm≤R_(ab)≤7.5 nm, and more preferably3.0 nm≤R_(ab)≤7.3 nm. The surface roughness R_(ab) within theabove-described value range contributes to improvement of handleabilityof the magnetic recording medium.

The surface roughness R_(ab) of the back layer may be more preferably7.2 nm or less, even more preferably 7.0 nm or less, 6.5 nm or less, 6.3nm or less, or 6.0 nm or less. The surface roughness R_(ab) may be morepreferably 3.2 nm or more, and even more preferably 3.4 nm or more. Thesurface roughness R_(ab) within the above-described value range,particularly not more than the upper limit improves the handleability,and achieves good electromagnetic conversion characteristic.

The method for measuring the surface roughness R_(ab) is described in2.(3) below.

The magnetic recording medium according to the present technology ispreferably a long magnetic recording medium, and may be, for example, amagnetic recording tape (particularly a long magnetic recording tape).

The magnetic recording medium according to the present technology mayinclude a magnetic layer, a base layer, and a back layer and may includeother layer as well as these layers. The other layer may be selected asappropriate according to the type of the magnetic recording medium. Themagnetic recording medium according to the present technology may be,for example, a magnetic recording medium of coating type or a magneticrecording medium of vacuum thin film type. The magnetic recording mediumof coating type is further described in detail in 2 below. The magneticrecording medium of vacuum thin film type is further described in detailin 3 and 4 below. See these descriptions for details about the layerother than these three layers included in the magnetic recording medium.

The magnetic recording medium according to the present technology mayinclude, for example, at least one data band and at least two servobands. The number of the data bands may be, for example, two to ten,particularly three to six, and more particularly four or five. Thenumber of the servo bands may be, for example, three to 11, particularlyfour to seven, and more particularly five or six. These servo bands anddata bands may be arranged, for example, so as to extend in thelongitudinal direction of, particularly in a generally parallel, to along magnetic recording medium (particularly a magnetic recording tape).The data band and the servo bands may be provided on the magnetic layer.Examples of the magnetic recording medium having the data band and theservo bands include magnetic recording tapes in conformity with thelinear tape-open (LTO) specification. More specifically, the magneticrecording medium according to the present technology may be a magneticrecording tape in conformity with the LTO specification. For example,the magnetic recording medium according to the present technology may bea magnetic recording tape in conformity with the LTO8 or laterspecifications (for example LTO9, LTO10, LTO11, or LTO12).

The width of the long magnetic recording medium (particularly magneticrecording tape) according to the present technology may be, for example5 mm to 30 mm, particularly 7 mm to 25 mm, more particularly 10 mm to 20mm, and even more particularly 11 mm to 19 mm. The length of the longmagnetic recording medium (particularly magnetic recording tape) may be,for example, 500 m to 1500 m. For example, the tape width and the tapelength according to the LTO8 specification are 12.65 mm and 960 m,respectively.

2. FIRST EMBODIMENT (EXAMPLE OF MAGNETIC RECORDING MEDIUM OF COATINGTYPE) (1) Configuration of Magnetic Recording Medium

Firstly, with reference to FIG. 1, the configuration of a magneticrecording medium 10 according to the first embodiment is described. Themagnetic recording medium 10 is, for example, a magnetic recordingmedium which has been subjected to vertical orienting treatment, andincludes, as depicted in FIG. 1, a long base layer (may be referred to amatrix) 11, a primary layer (non-magnetic layer) 12 provided on one mainsurface of the base layer 11, a magnetic layer (may be referred to as arecording layer) 13 provided on the primary layer 12, and a back layer14 provided on the other main surface of the base layer 11. Of the mainsurfaces of the magnetic recording medium 10, the surface having themagnetic layer 13 is referred to as a magnetic surface, and the surfaceopposite to the magnetic surface (the surface having the back layer 14)is referred to as a back surface.

The magnetic recording medium 10 is long, and traveled in thelongitudinal direction during recording and reproducing. Additionally,the magnetic recording medium 10 may be configured so as to record asignal at the shortest recording wavelength of preferably 100 nm orless, more preferably 75 nm or less, even more preferably 60 nm or less,and particularly preferably 50 nm or less, and may be used in, forexample, a recording and reproducing apparatus in which the shortestrecording wavelength is within the above-described range. The recordingand reproducing apparatus may include a ring-shaped head as a recordinghead. The recording track width is, for example 2 μm or less.

(2) Description of Each Layer

(Base layer)

The base layer 11 can work as a support of the magnetic recording medium10, and may be, for example, a flexible long non-magnetic matrix,particularly a non-magnetic film. The thickness of the base layer 11 maybe, for example, 2 μm or more 8 μm or less, preferably 2.2 μm or more 7μm or less, more preferably 2.5 μm or more 6 μm or less, and even morepreferably 2.6 μm or more 5 μm or less. The base layer 11 may include atleast one of, for example, polyester resins, polyolefin resins,cellulose derivatives, vinyl resins, aromatic polyether ketone resins,or other polymer resins. In a case where the base layer 11 includes twoor more of the above materials, these two or more materials may bemixed, copolymerized, or laminated.

Examples of the polyester resin include polyethylene terephthalate(PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT),polybutylene naphthalate (PBN), polycyclohexylene dimethyleneterephthalate (PCT), polyethylene-p-oxybenzoate (PEB), and polyethylenebisphenoxy carboxylate, which may be used alone or in combination of twoor more of them. According to a preferred embodiment of the presenttechnology, the base layer 11 may include PET or PEN.

Examples of the polyolefin resin include polyethylene (PE) andpolypropylene (PP), which may be used alone or in combination of two ormore of them.

Examples of the cellulose derivative include cellulose diacetate,cellulose triacetate, cellulose acetate butylate (CAB), and celluloseacetate propionate (CAP), which may be used alone or in combination oftwo or more of them.

Examples of the vinyl resin include polyvinyl chloride (PVC) andpolyvinylidene chloride (PVDC), which may be used alone or incombination of two or more of them.

Examples of the aromatic polyether ketone resin include polyether ketone(PEK), polyether ether ketone (PEEK), polyether ketone (PEKK), andpolyether ether ketone (PEEKK), which may be used alone or incombination of two or more of them. According to a preferred embodimentof the present technology, the base layer 11 may include PEEK.

Examples of the other polymer resin include polyamide ((PA), nylon),aromatic PA (aromatic polyamide, aramid), polyimide (PI), aromatic PI(aromatic polyimide), polyamide imide (PAI), aromatic PAI (aromaticpolyamide imide), polybenzoxazole ((PBO), for example ZYLON (registeredtrademark)), polyether, polyether ester, polyether sulfone (PES),polyether imide (PEI), polysulfone (PSF), polyphenylene sulfide (PPS),polycarbonate (PC), polyarylate (PAR), and polyurethane (PU), which maybe used alone or in combination of two or more of them.

(Magnetic Layer)

The magnetic layer 13 may be, for example, a vertical recording layer.The magnetic layer 13 may include a magnetic powder. The magnetic layer13 may further include, in addition to the magnetic powder, for example,a binder and conductive particles. The magnetic layer 13 may furtherinclude, as necessary, additives such as a lubricant, an abrasive, and arust-preventive agent.

The average thickness t_(m) of the magnetic layer 13 may be preferably35 nm≤t_(m)≤120 nm, more preferably 35 nm≤t_(m)≤100 nm, and particularlypreferably 35 nm≤t_(m)≤90 nm. The average thickness t_(m) of themagnetic layer 13 within the above-described value range contributes toimprovement of the electromagnetic conversion characteristic.

The average thickness t_(m) of the magnetic layer 13 is determined asfollows. Firstly, the magnetic recording medium 10 is thinly processedperpendicularly to its main surface to make a sample piece, and a crosssection of the test piece is observed with a transmission electronmicroscope (TEM) under the following conditions.

Apparatus: TEM (Hitachi, Ltd., H9000NAR)

Accelerating voltage: 300 kV

Magnification: 100,000 times

Subsequently, using the TEM image thus obtained, the thickness of themagnetic layer 13 is measured at least ten points in the longitudinaldirection of the magnetic recording medium 10, and then thesemeasurement values are simply averaged (arithmetically averaged) toobtain the average thickness t_(m) (nm) of the magnetic layer 13.

The magnetic layer 13 is preferably a vertically oriented magneticlayer. In the present description, vertical orientation means that thesquareness ratio S1 measured in the longitudinal direction (travelingdirection) of the magnetic recording medium 10 is 35% or less. Themethod for measuring the squareness ratio S1 is described below.

Note that the magnetic layer 13 may be an in-plane oriented(longitudinally oriented) magnetic layer. More specifically, themagnetic recording medium 10 may be a magnetic recording medium ofhorizontal recording type. However, vertical orientation is morepreferred for achieving a high recording density.

(Magnetic Powder)

Examples of the magnetic particles composing the magnetic powderincluded in the magnetic layer 13 include, but not limited to, anepsilon iron oxide (ε-iron oxide), gamma hematite, magnetite, chromiumdioxide, cobalt-doped iron oxide, hexagonal ferrite, barium ferrite(BaFe), Co ferrite, strontium ferrite, and metal. The magnetic powdermay be one of them or a combination of two or more of them. Particularlypreferably, the magnetic powder may include an ε-iron oxide magneticpowder, a barium ferrite magnetic powder, a cobalt ferrite magneticpowder, or a strontium ferrite magnetic powder. Note that the ε-ironoxide may include Ga and/or Al. These magnetic particles may be selectedas appropriate by those skilled in the art on the basis of factors, forexample, the method for producing the magnetic layer 13, thespecification of the tape, and the function of the tape.

The average particle size (average maximum particle size) D of themagnetic powder may be preferably 22 nm or less, more preferably 8 nm ormore and 22 nm or less, and even more preferably 10 nm or more and 20 nmor less.

The average particle size D of the magnetic powder is determined asfollows. Firstly, the magnetic recording medium 10 to be measured isprocessed by, for example, the focused ion beam (FIB) method to make aslice, and a cross section of the slice is observed with a TEM.

Subsequently, 500 ε-iron oxide particles are randomly selected from theTEM photograph thus shot, the maximum particle size d_(max) of eachparticle is measured, thereby determining the particle size distributionof the maximum particle size d_(max) of the magnetic powder. The term“maximum particle size d_(max)” means the so-called maximum Feretdiameter, specifically, refers to the maximum one of the distancesbetween two parallel lines drawn at every angle so as to be in contactwith the contour of ε-iron oxide particles. Thereafter, the mediandiameter (50% diameter, D50) of the maximum particle size d_(max) isdetermined from the particle size distribution of the maximum particlesize d_(max) thus determined, and recorded as the average particle size(average maximum particle size) D of the magnetic powder.

The shape of the magnetic particles depends on the crystal structure ofthe magnetic particles. For example, BaFe and strontium ferrite may havea hexagonal plate shape. ε-iron oxide may have a spherical shape. Cobaltferrite may have a cubic shape. Metal may have a spindle shape. Thesemagnetic particles are oriented in the production process of themagnetic recording medium 10.

According to a preferred embodiment of the present technology, themagnetic powder may preferably include the powder of nanoparticlesincluding ε-iron oxide (hereinafter referred to as “ε-iron oxideparticles”). ε-iron oxide particles can achieve high coercivity even inthe form of fine particles. The ε-iron oxide included in ε-iron oxideparticles is preferably preferentially crystal-oriented in the thicknessdirection (vertical direction) of the magnetic recording medium 10.

The ε-iron oxide particles have a spherical or generally sphericalshape, or a cubic or generally cubic shape. Since the ε-iron oxideparticles have the above-described shape, in a case where F-iron oxideparticles are used as magnetic particles, the contact area betweenparticles in the thickness direction of the medium is reduced incomparison with the case where hexagonal lamellar barium ferriteparticles are used as magnetic particles, and thus flocculation ofparticles is suppressed. Accordingly, dispersibility of the magneticpowder is increased, and better signal-to-noise ratio (SNR) is obtained.

The ε-iron oxide particles have a core-shell structure. Specifically,the ε-iron oxide particles include, as depicted in FIG. 2, a core 21,and a shell 22 with a two-layer structure formed around the core 21. Theshell 22 with a two-layer structure includes a first shell 22 a providedon the core 21, and a second shell 22 b provided on the first shell 22a.

The core 21 includes ε-iron oxide. The ε-iron oxide included in the core21 preferably includes ε-Fe₂O₃ crystals as the main phase, and morepreferably includes ε-Fe₂O₃ of single phase.

The first shell 22 a covers at least a portion of the periphery of thecore 21. Specifically, the first shell 22 a may partially cover theperiphery of the core 21, or the entire periphery of the core 21. It ispreferred that the entire surface of the core 21 be covered forachieving sufficient exchange coupling between the core 21 and the firstshell 22 a, and improving the magnetic characteristic. The first shell22 a is a so-called soft magnetic layer, and may include, for example, asoft magnetic substance such as α-Fe, Ni—Fe alloy, or Fe—Si—Al alloy.α-Fe may be obtained by reducing ε-iron oxide included in the core 21.

The second shell 22 b is an oxide film as an oxidation preventive layer.The second shell 22 b may include α-iron oxide, aluminum oxide, orsilicon oxide. The α-iron oxide may include, for example, at least oneiron oxide of Fe₃O₄, Fe₂O₃, and FeO. In a case where the first shell 22a includes α-Fe (soft magnetic substance), the α-iron oxide may beobtained by oxidizing α-Fe included in the first shell 22 a.

Inclusion of the first shell 22 a in the ε-iron oxide particles asdescribed above allows achievement of thermal stability, and thus thiskeeps the coercivity He of the core 21 alone at a high value and/oradjusts the coercivity He of the entire ε-iron oxide particles(core-shell particles) at the coercivity He suitable for recording.Additionally, Inclusion of the second shell 22 b in the ε-iron oxideparticles as described above suppresses the deterioration incharacteristics of the ε-iron oxide particles caused by rust on theparticle surface generated by exposure of the F-iron oxide particles toair during and before the production process of the magnetic recordingmedium 10. Accordingly, deterioration of characteristics of the magneticrecording medium 10 is suppressed.

The ε-iron oxide particles may include, as depicted in FIG. 6, a shell23 with a monolayer structure. In this case, the shell 23 has aconfiguration similar to the first shell 22 a. However, from theviewpoint of suppressing deterioration of characteristics of the ε-ironoxide particles, the ε-iron oxide particles more preferably include ashell 22 having a two-layer structure.

The ε-iron oxide particles may include an additive in place of acore-shell structure, or may include an additive besides a core-shellstructure. In these cases, a portion of Fe of the ε-iron oxide particlesis substituted with the additive. The inclusion of an additive in theε-iron oxide particles adjusts the coercivity He of the entire ε-ironoxide particles to the coercivity He suitable for recording, and thusimproves recording easiness. The additive is a metal element other thaniron, preferably a trivalent metal element, more preferably at least oneselected from the group including aluminum (Al), gallium (Ga), andindium (In).

Specifically, the ε-iron oxide including an additive isε-Fe_(2-x)M_(x)O₃ crystal (in which M is a metal element other thaniron, preferably a trivalent metal element, more preferably at least oneselected from the group including Al, Ga, and In; x is, for example,0<x<1).

According to another preferred embodiment of the present technology, themagnetic powder may be a barium ferrite (BaFe) magnetic powder. Thebarium ferrite magnetic powder includes magnetic particles of iron oxideincluding barium ferrite as the main phase (hereinafter referred to as“barium ferrite particles”). The barium ferrite magnetic powder has highreliability of data recording, for example, retention of antimagneticforce even in a high temperature and high humidity environment. Fromthese viewpoints, the barium ferrite magnetic powder is preferred as themagnetic powder.

The average particle size of the barium ferrite magnetic powder is 50 nmor less, more preferably 10 nm or more and 40 nm or less, and even morepreferably 12 nm or more and 25 nm or less. In a case where the magneticlayer 13 includes a barium ferrite magnetic powder as a magnetic powder,the average thickness t_(m) [nm] of the magnetic layer 13 is preferably35 nm≤t_(m)≤100 nm. In addition, the coercivity He of the magneticrecording medium 10 measured in the thickness direction (verticaldirection) is preferably 160 kA/m or more and 280 kA/m or less, morepreferably 165 kA/m or more and 275 kA/m or less, and even morepreferably 170 kA/m or more and 270 kA/m or less.

According to a more preferred other embodiment of the presenttechnology, the magnetic powder may be a cobalt ferrite magnetic powder.The cobalt ferrite magnetic powder includes magnetic particles of ironoxide including cobalt ferrite as the main phase (hereinafter referredto as “cobalt ferrite magnetic particles”). The cobalt ferrite magneticparticles preferably has uniaxial anisotropy. The cobalt ferritemagnetic particles have, for example, a cubic or generally cubic shape.The cobalt ferrite includes Co. The cobalt ferrite may further include,in addition to Co, at least one selected from the group including Ni,Mn, Al, Cu, and Zn.

The cobalt ferrite has the average composition represented by, forexample, the following formula (1).Co_(x)M_(y)Fe₂O_(z)  (1)

(In the formula (1), M is, for example, at least one metal selected fromthe group including Ni, Mn, Al, Cu, and Zn; x is a value within therange of 0.4≤x≤1.0. y is a value within the range of 0≤y≤0.3; x and ysatisfy the relationship (x+y)≤1.0; z is a value within the range of3≤z≤4; a portion of Fe may be substituted with other metal element.) Theaverage particle size of the cobalt ferrite magnetic powder ispreferably 25 nm or less, and more preferably 23 nm or less. Thecoercivity He of the cobalt ferrite magnetic powder is preferably 2500Oe or more, and more preferably 2600 Oe or more and 3500 Oe or less.According to more preferred other embodiment of the present technology,the magnetic powder may include the powder of nanoparticles of hexagonalferrite (hereinafter referred to as “hexagonal ferrite particles”). Thehexagonal ferrite particles include, for example, hexagonal plate-shapedor generally hexagonal plate-shaped. The hexagonal ferrite preferablyincludes at least one of Ba, Sr, Pb, or Ca, and more preferably at leastone of Ba or Sr. The hexagonal ferrite may be, specifically, forexample, barium ferrite or strontium ferrite. The barium ferrite mayfurther include, in addition to Ba, at least one of Sr, Pb, or Ca. Thestrontium ferrite may further include, in addition to Sr, at least oneof Ba, Pb, or Ca.

More specifically, the hexagonal ferrite may have an average compositionrepresented by the general formula MFe₁₂O₁₉, in which M is, for example,at least one metal of Ba, Sr, Pb, or Ca, and preferably at least onemetal of Ba or Sr. The M may be a combination of Ba and at least onemetal selected from the group including Sr, Pb, and Ca. Furthermore, theM may be a combination of Sr and at least one metal selected from thegroup including Ba, Pb, and Ca. In the general formula, a portion of Femay be substituted with other metal element.

In a case where the magnetic powder includes the powder of hexagonalferrite particles, the average particle size of the magnetic powder ispreferably 50 nm or less, more preferably 10 nm or more and 40 nm orless, and even more preferably 15 nm or more and 30 nm or less.

(Binder)

The binder is preferably, for example, a polyurethane resin or a vinylchloride resin subjected to crosslinking reaction. However, the binderwill not be limited to them, and may include other resin as appropriateaccording to the physical properties which may be required of themagnetic recording medium 10. The resin to be included will not beparticularly limited as long as it is usually used in the magneticrecording medium 10 of coating type.

Examples of the binder include polyvinyl chloride, polyvinyl acetate, avinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinylidenechloride copolymer, a vinyl chloride-acrylonitrile copolymer, anacrylate-acrylonitrile copolymer, an acrylate-vinyl chloride-vinylidenechloride copolymer, a vinyl chloride-acrylonitrile copolymer, anacrylate-acrylonitrile copolymer, an acrylate-vinylidene chloridecopolymer, a methacrylate-vinylidene chloride copolymer, amethacrylate-vinyl chloride copolymer, a methacrylate-ethylenecopolymer, polyvinyl fluoride, a vinylidene chloride-acrylonitrilecopolymer, an acrylonitrile-butadiene copolymer, a polyamide resin,polyvinyl butyral, cellulose derivatives (cellulose acetate butylate,cellulose diacetate, cellulose triacetate, cellulose propionate, andnitrocellulose), a styrene butadiene copolymer, a polyester resin, anamino resin, and synthetic rubber.

Additionally, the binder may be a thermosetting resin or a reactiveresin, and examples of them include a phenolic resin, an epoxy resin, anurea resin, a melamine resin, an alkyd resin, a silicone resin, apolyamine resin, and an urea formaldehyde resin.

Additionally, the above-listed binders may include a polar functionalgroup such as —SO₃M, —OSO₃M, —COOM, P═O(OM)₂ for the purpose ofimproving dispersibility of the magnetic powder.

Here, in the formula, M is a hydrogen atom, or an alkali metal such aslithium, potassium, and sodium.

Additionally, examples of the polar functional group include those ofside chain type having end groups —NR1R2 and —NR1R2R3⁺X⁻, and those ofmain chain type having >NR1R2⁺X⁻.

Here, in the formula, R1, R2, and R3 are hydrogen atoms or hydrocarbongroups, and X⁻ is a halogen element ion such as fluorine, chlorine,bromine, or iodine, or an inorganic or organic ion. Additionally,examples of the polar functional group include —OH, —SH, —CN, and anepoxy group.

(Additive)

The magnetic layer 13 may further include, as non-magnetic reinforcingparticles, aluminum oxide (α, β, or γ-alumina), chromic oxide, siliconoxide, diamond, garnet, emery, boron nitride, titanium carbide, siliconcarbide, titanium carbide, titanium oxide (rutile type or anatase typetitanium oxide).

(Primary Layer)

The primary layer 12 is a non-magnetic layer including a non-magneticpowder and a binder as main ingredients. The description about thebinder included in the magnetic layer 13 also holds true for the binderincluded in the primary layer 12. The primary layer 12 may furtherinclude, as necessary, at least one additive such as conductiveparticles, a lubricant, a curing agent, and a rust-preventive agent.

The average thickness of the primary layer 12 is preferably 0.6 μm ormore and 2.0 μm or less, more preferably 0.8 μm or more and 1.4 μm orless. Note that the average thickness of the primary layer 12 isdetermined in a manner similar to the average thickness t_(m) of themagnetic layer 13. However, the magnification of the TEM image isappropriately adjusted according to the thickness of the primary layer12.

(Non-Magnetic Powder)

The non-magnetic powder included in the primary layer 12 may include,for example, at least one selected from inorganic particles and organicparticles. One kind of non-magnetic powder may be used alone, or acombination of two or more kinds of non-magnetic powder may be used. Theinorganic particles include, for example, one or a combination of two ormore selected from metal, metal oxide, metal carbonate, metal sulfate,metal nitride, metal carbide, and metal sulfide. More specifically, theinorganic particles may be, for example, one or more selected from ironoxyhydroxide, hematite, titanium oxide, and carbon black. Examples ofthe shape of the non-magnetic powder include, but not particularlylimited to, various shapes such as a needle shape, a spherical shape, acubic shape, and a plate shape.

(Back Layer)

The back layer 14 may include a binder and a non-magnetic powder. Theback layer 14 may include, as necessary, various additives such as alubricant, a curing agent, and an antistatic agent. The statements aboutthe binder and the non-magnetic powder included in the primary layer 12apply to the binder and the non-magnetic powder included in the backlayer 14.

The average particle size of the inorganic particles included in theback layer 14 is preferably 10 nm or more and 150 nm or less, and morepreferably 15 nm or more and 110 nm or less. The average particle sizeof the inorganic particles can be determined in a manner similar to theaverage particle size D of the magnetic powder.

The average thickness t_(b) of the back layer 14 is preferably t_(b)≤0.6μm. The average thickness t_(b) of the back layer 14 within theabove-described range allows the thicknesses of the primary layer 12 andthe base layer 11 to be kept high even if the average thickness t_(T) ofthe magnetic recording medium 10 is t_(T)≤5.5 μm, and this maintainstraveling stability of the magnetic recording medium 10 in a recordingand reproducing apparatus.

The average thickness t_(b) of the back layer 14 is determined asfollows. Firstly, the magnetic recording medium 10 with a width of ½inches is provided, cut into a piece with a length of 250 mm, thusmaking a sample. Subsequently, using Mitsutoyo Laser Hologage as ameasuring apparatus, the thickness of the sample is measured atdifferent five points, and these measurement values are simply averaged(arithmetically averaged), thereby calculating the average t_(T) [μm].Subsequently, the back layer 14 of the sample is removed with a solventsuch as methyl ethyl ketone (MEK) or dilute hydrochloric acid, and thenthe thickness of the sample is measured again at different five pointsusing the above-described Laser Hologage, and these measurement valuesare simply averaged (arithmetically averaged), thereby calculating theaverage t_(B) [μm]. Subsequently, the average thickness t_(b) of theback layer 14 (μm) is determined by the following formula.t _(b) [μm]=t _(T) [μm]−t _(B) [μm]

(3) Physical Properties and Structure

(Average Thickness t_(T) of Magnetic Recording Medium)

The average thickness t_(T) of the magnetic recording medium 10 ist_(T)≤5.5 μm. If the average thickness t_(T) of the magnetic recordingmedium 10 is t_(T)≤5.5 μm, the recording capacity of one data cartridgeis increased from that of related art. The lower limit of the averagethickness t_(T) of the magnetic recording medium 10 is not particularlylimited, and is, for example, 3.5 μm≤t_(T). The average thickness t_(T)of the magnetic recording medium 10 is determined by the method formeasuring the average t_(T), which has been described in the method formeasuring the average thickness t_(b) of the back layer 14.

(Dimensional Variation Δw)

The dimensional variation Δw [ppm/N] of the magnetic recording medium 10in the width direction to the tension change of the magnetic recordingmedium 10 in the longitudinal direction is 650 ppm/N≤Δw, more preferably670 ppm/N≤Δw, more preferably 700 ppm/N≤Δw, more preferably 710ppm/N≤Δw, more preferably 730 ppm/N≤Δw, more preferably 750 ppm/N≤Δw,even more preferably 780 ppm/N≤Δw, and particularly preferably 800ppm/N≤Δw. If the dimensional variation Δw is Δw≤640 ppm/N, suppressionof width change through the adjustment of the tension in thelongitudinal direction with the recording and reproducing apparatus maybe difficult. The upper limit of the dimensional variation Δw is notparticularly limited, and, for example, may be Δw≤1700000 ppm/N,preferably Δw≤20000 ppm/N, more preferably Δw≤8000 ppm/N, and even morepreferably Δw≤5000 ppm/N, Δw≤4000 ppm/N, Δw≤3000 ppm/N, or Δw≤2000ppm/N.

Those skilled in the art may set the dimensional variation Δw as needed.For example, the dimensional variation Δw may be set at a desired valueby selecting the thickness of the base layer 11 and/or the material ofthe base layer 11. Additionally, the dimensional variation Δw may be setat a desired value by, for example, adjusting the stretch strength ofthe film composing the base layer in the longitudinal and lateraldirections. For example, the Δw further decreases by strongly drawing inthe width direction, while the Δw increases by strongly drawing in thelongitudinal direction.

The dimensional variation Δw is determined as follows. Firstly, themagnetic recording medium 10 having a width of ½ inches is provided, cutinto a piece having a length of 250 mm, thus making a sample 10S.Secondly, loads of 0.2 N, 0.6 N, and 1.0 N are applied in this order tothe sample 10S in the longitudinal direction, and the width of thesample 10S is measured under the loads of 0.2N, 0.6N, and 1.0 N.Subsequently, the dimensional variation Δw is determined by thefollowing formula. Note that the measurement under application of a loadof 0.6 N is carried out for confirming that no abnormality occurred inthe measurement (particularly, for confirming that these threemeasurement results are linear), and the measurement result is not usedin the following formula.

$\begin{matrix}{{\Delta\;{w\lbrack {{ppm}\text{/}N} \rbrack}} = {\frac{{{D( {0.2N} )}\lbrack{mm}\rbrack} - {{D( {1.0N} )}\lbrack{mm}\rbrack}}{{D( {0.2N} )}\lbrack{mm}\rbrack} \times \frac{1\text{,}000\text{,}000}{( {1.0\lbrack N\rbrack} ) - ( {0.2\lbrack N\rbrack} )}}} & \lbrack {{Math}.\mspace{14mu} 1} \rbrack\end{matrix}$

(Note that in the formula, D(0.2 N) and D(1.0 N) represent the widths ofthe sample 10S subjected to loads of 0.2 N and 1.0 N, respectively, inthe longitudinal direction of the sample 10S.)

The width of the sample 10S subjected to each load is measured asfollows. Firstly, as measuring apparatus, the measuring apparatusdepicted in FIG. 3A including the digital dimension measuring instrumentLS-7000 manufactured by KEYENCE CORPORATION is provided, and the sample10S is mounted on the measuring apparatus. Specifically, one end of thelong sample (magnetic recording medium) 10S is fixed by a fixing unit231. Subsequently, as depicted in FIG. 3A, the sample 10S is mounted onfive generally columnar and rod-like support members 232. The sample 10Sis mounted on these supports in such a manner that the back surface isin contact with the five support members 232. All of the five supportmembers 232 (particularly their surfaces) include stainless steelSUS304, and their surface roughness Rz (maximum height) is 0.15 μm to0.3 μm.

The arrangement of the five rod-like support members 232 is describedwith reference to FIG. 3B. As depicted in FIG. 3B, the sample 10S ismounted on the five support members 232. The five support members 232are referred to as, from the one nearest to the fixing unit 231, “firstsupport member”, “second support member”, “third support member” (havinga slit 232A), “fourth support member”, and “fifth support member”(closest to a weight 233). The diameter of these five support members is7 mm. The distance d₁ between the first support member and the secondsupport member (particularly the distance between the centers of thesesupport members) is 20 mm. The distance d₂ between the second supportmember and the third support member is 30 mm. The distance d₃ betweenthe third support member and the fourth support member is 30 mm. Thedistance d₄ between the fourth support member and the fifth supportmember is 20 mm. Additionally, in the sample 10S, the second supportmember, the third support member, and the fourth support member arearranged in such a manner that the portions mounted on the positionbetween the second support member, the third support member, and thefourth support member form a flat surface generally perpendicular to thedirection of gravitational force. Additionally, the first support memberand the second support member are arranged in such a manner that thesample 10S forms an angle of θ₁=30° to the generally vertical flatsurface between the first support member and the second support member.Furthermore, the fourth support member and the fifth support member arearranged in such a manner that the sample 10S forms an angle of θ₂=30°to the generally vertical flat surface between the fourth support memberand the fifth support member.

Additionally, of the five support members 232, the third support memberis fixed so as not to rotate, but all of the other four support membersare rotatable.

The sample 10S is held on the support members 232 so as not to move inthe width direction of the sample 10S. Note that, of the support members232, the support member 232, which is located between a light emitter234 and a light receiver 235, and at the almost middle of the fixingunit 231 and the loading unit, has the slit 232A. Light L is emittedfrom the light emitter 234 to the light receiver 235 through the slit232A. The slit width of the slit 232A is 1 mm, and the light L passesthrough the width without being blocked by the frame of the slit 232A.Subsequently, the measuring apparatus is placed in a chamber controlledat a constant environment having a temperature of 25° C. and a relativehumidity of 50%, the weight 233 for applying a load of 0.2 N is attachedto the other end of the sample 10S, and then the sample 10S is allowedto stand in the environment for two hours. After standing for two hours,the width of the sample 10S is measured. Subsequently, the weight forapplying a load of 0.2 N is replaced with a weight for applying a loadof 0.6 N, and the width of the sample 10S is measured five minutes afterthe replacement. Finally, the weight is replaced with a weight forapplying a load of 1.0 N, and the width of the sample 10S is measuredfive minutes after the replacement.

As described above, the load applied to the longitudinal direction ofthe sample 10S can be changed by adjusting the weight of the weight 233.The light L is emitted from the light emitter 234 to the light receiver235 with each load applied, and the width of the sample 10S subjected tothe load in the longitudinal direction is measured. Measurement of thewidth is carried out in a condition where the sample 10S is not curled.The light emitter 234 and the light receiver 235 are included in thedigital dimension measuring instrument LS-7000.

(Thermal Expansion Coefficient α)

The thermal expansion coefficient α [ppm/° C.] of the magnetic recordingmedium 10 may be preferably 5.5 ppm/° C.≤α≤9 ppm/° C., and morepreferably 5.9 ppm/° C.≤α≤8 ppm/° C. The thermal expansion coefficient αwithin the above-described range allows the width change of the magneticrecording medium 10 to be further suppressed through the adjustment ofthe tension of the magnetic recording medium 10 in the longitudinaldirection with a recording and reproducing apparatus.

The thermal expansion coefficient α can be determined as follows.Firstly, a sample 10S is made in a manner similar to the method formeasuring the dimensional variation Δw, the sample 10S is mounted on ameasuring apparatus similar to that used in the method for measuring thedimensional variation Δw, and the measuring apparatus is placed in achamber having a constant environment with a temperature of 29° C. and arelative humidity of 24%. Secondly, a load of 0.2 N is applied to thesample 10S in the longitudinal direction, and the sample 10S is allowedto stand in the environment for two hours. Thereafter, with the relativehumidity kept at 24%, the temperature is changed to 45° C., 29° C., and10° C. in this order, the width of the sample 10S is measured at 45° C.,29° C., and 10° C., and the thermal expansion coefficient α isdetermined by the following formula. The measurement at thesetemperatures is carried out two hours after reaching each temperature.Note that the measurement at a temperature of 29° C. is carried out forconfirming that no abnormality occurred in the measurement(particularly, for confirming that these three measurement results arelinear), and the measurement result is not used in the followingformula.

$\begin{matrix}{{\alpha\mspace{14mu}\lbrack {{ppm}\text{/}{^\circ}\mspace{14mu}{C.}} \rbrack} = {\frac{{{D( {45{^\circ}\mspace{14mu}{C.}} )}\lbrack{mm}\rbrack} - {{D( {10{^\circ}\mspace{14mu}{C.}} )}\lbrack{mm}\rbrack}}{{D( {10{^\circ}\mspace{14mu}{C.}} )}\lbrack{mm}\rbrack} \times \frac{1\text{,}000\text{,}000}{( {45\lbrack {{^\circ}\mspace{14mu}{C.}} \rbrack} ) - ( {10\lbrack {{^\circ}\mspace{14mu}{C.}} \rbrack} )}}} & \lbrack {{Math}.\mspace{14mu} 2} \rbrack\end{matrix}$

(Note that in the formula, D(45° C.) and D(10° C.) represent the widthsof the sample 10S at the temperatures of 45° C. and 10° C.,respectively.)

(Humidity Expansion Coefficient β)

The humidity expansion coefficient β [ppm/% RH] of the magneticrecording medium 10 may be preferably β≤5.5 ppm/% RH, more preferablyβ≤5.2 ppm/% RH, and even more preferably β≤5.0 ppm/% RH. The humidityexpansion coefficient β within the above-described range furthersuppresses the width change of the magnetic recording medium 10 throughadjustment of the tension of the magnetic recording medium 10 in thelongitudinal direction with a recording and reproducing apparatus.

The humidity expansion coefficient β is determined as follows. Firstly,a sample 10S is made in a manner similar to the method for measuringdimensional variation Δw, and the sample 10S is mounted on a measuringapparatus similar to that used in the method for measuring dimensionalvariation Δw, and then the measuring apparatus is placed in a chambercontrolled at a constant environment having a temperature of 29° C. anda relative humidity of 24%. Subsequently, a load of 0.2 N is applied tothe sample 10S in the longitudinal direction, and the sample is placedin this environment for two hours. Thereafter, the relative humidity ischanged to 80%, 24%, and 10% in this order with the temperature kept at29° C., the width of the sample 10S is measured at the relativehumidities of 80%, 24%, and 10%, and the humidity expansion coefficientβ is determined by the following formula. The measurement at thesehumidity values is carried out immediately after each temperature isattained. Note that the measurement at humidity of 24% is carried outfor confirming that no abnormality occurred in the measurement, and itsmeasurement result is not used in the following formula.

$\begin{matrix}{{\beta\mspace{14mu}\lbrack {{ppm}\text{/}\%{RH}} \rbrack} = {\frac{{{D( {80\%} )}\lbrack{mm}\rbrack} - {{D( {10\%} )}\lbrack{mm}\rbrack}}{{D( {10\%} )}\lbrack{mm}\rbrack} \times \frac{1\text{,}000\text{,}000}{( {80\lbrack\%\rbrack} ) - ( {10\lbrack\%\rbrack} )}}} & \lbrack {{Math}.\mspace{14mu} 3} \rbrack\end{matrix}$

(Note that in the formula, D(80%) and D(10%) represent the widths of thesample 10S at the humidities of 80% and 10%, respectively)

(Poisson's Ratio ρ)

The Poisson's ratio ρ of the magnetic recording medium 10 may bepreferably 0.25≤ρ, more preferably 0.29≤ρ, and even more preferably0.3≤ρ. If the Poisson's ratio ρ is within the above-described range,width change of the magnetic recording medium 10 through the adjustmentof the tension of the magnetic recording medium 10 in the longitudinaldirection with a recording and reproducing apparatus is facilitated.

The Poisson's ratio ρ is determined as follows. Firstly, a magneticrecording medium 10 having a width of ½ inches is provided, cut into apiece having a length of 150 mm to make a sample, and then a mark with asize of 6 mm×6 mm is made at the center of the sample. Subsequently,both the ends of the sample in the longitudinal direction are chucked insuch a manner that the distance between the chucks is 100 mm, an initialload of 2 N is applied. At this time, the mark length on the sample inthe longitudinal direction is recorded as the initial length, and themark width on the sample in the width direction is recorded as theinitial width. Subsequently, the sample is pulled at a pulling speed of0.5 mm/min using a universal tensile testing apparatus of Instron type,and the dimensional variations of the mark length of the sample in thelongitudinal direction and the mark width of the sample in the widthdirection are measured using an image sensor of KEYENCE CORPORATION.Thereafter, the Poisson's ratio ρ is determined by the followingformula.

$\begin{matrix}{\rho = \frac{\{ \frac{\begin{matrix}( {{Dimensional}\mspace{14mu}{variation}\mspace{14mu}{of}}  \\ {{mark}\mspace{14mu}{{width}\mspace{14mu}\lbrack{mm}\rbrack}} )\end{matrix}}{( {{Initial}\mspace{14mu}{{width}\mspace{14mu}\lbrack{mm}\rbrack}} )} \}}{\{ \frac{\begin{matrix}( {{Dimensional}\mspace{14mu}{variation}\mspace{14mu}{of}}  \\ {{mark}\mspace{14mu}{{length}\mspace{14mu}\lbrack{mm}\rbrack}} )\end{matrix}}{( {{Initial}\mspace{14mu}{{length}\mspace{14mu}\lbrack{mm}\rbrack}} )} \}}} & \lbrack {{Math}.\mspace{14mu} 4} \rbrack\end{matrix}$

(Elastic Limit Value σ_(MD) in the Longitudinal Direction)

The elastic limit value σ_(MD) [N] of the magnetic recording medium 10in the longitudinal direction may be preferably 0.7 N≤σ_(MD), morepreferably 0.75 N≤σ_(MD), and even more preferably 0.8 N≤σ_(MD). If theelastic limit value σ_(MD) is within the above-described range, widthchange of the magnetic recording medium 10 is further suppressed throughadjustment of the tension of the magnetic recording medium 10 in thelongitudinal direction with a recording and reproducing apparatus.Additionally, control of the drive side is facilitated. The upper limitof the elastic limit value σ_(MD) of the magnetic recording medium 10 inthe longitudinal direction is not particularly limited, and is, forexample, σ_(MD)≤5.0 N. The elastic limit value σ_(MD) preferably doesnot depend on the velocity V in the measurement of elastic limit. Thereason for this is that independence of the elastic limit value σ_(MD)from the velocity V allows effective suppression of width change of themagnetic recording medium 10 without being influenced by the travelingvelocity of the magnetic recording medium 10 in a recording andreproducing apparatus, and the tension adjustment velocity and itsresponsiveness of the recording and reproducing apparatus. The elasticlimit value σ_(MD) is set at a desired value according to, for example,the selection of the curing conditions of the primary layer 12, themagnetic layer 13, and the back layer 14, and/or the selection of thematerial of the base layer 11. For example, with the increase of thecuring time of the primary layer forming paint, the magnetic layerforming paint, and the back layer forming paint, or with the increase ofthe curing temperature, the reaction between the binder and the curingagent included in each paint is accelerated. This improves the elasticcharacteristic and the elastic limit value σ_(MD).

The elastic limit value σ_(MD) can be determined as follows. Firstly, amagnetic recording medium 10 having a width of ½ inches is provided, cutinto a piece having a length of 150 mm, thus making a sample. The bothends of the sample in the longitudinal direction are chucked with auniversal tensile test apparatus in such a manner that the distancebetween the chucks λ₀ is λ₀=100 mm. Secondly, the sample is pulled at apulling speed of 0.5 mm/min, and the load σ (N) to the distance betweenthe chucks λ (mm) is continuously measured. Subsequently, using the dataof λ (mm) and σ (N) thus obtained, the relationship between Δλ (%) and σ(N) are graphed.

The Δλ (%) is obtained by the following formula.Δλ(%)=((λ−λ₀)/λ₀)×100

Subsequently, in the region of σ≥0.2 N in the above graph, the regionwhere the graph is a straight line is calculated, and the maximum load σis recorded as the elastic limit value σ_(MD) (N).

(Coefficient of Friction μ Between Magnetic Surface and Back Surface)

The coefficient of friction μ between the surface of the magneticrecording medium 10 on the magnetic layer side and the surface on theback layer side (hereinafter may be referred to as “coefficient ofinterlayer friction μ”) is preferably 0.20≤μ≤0.80, and more preferably0.20≤μ≤0.78, even more preferably 0.25≤μ≤0.75. The coefficient offriction μ is within the above-described range improves handleability ofthe magnetic recording medium 10. For example, the coefficient offriction μ within the above-described range suppresses, for example, theoccurrence of winding deviation during winding of the magnetic recordingmedium 10 on a reel (for example, the reel 10C in FIG. 5). Morespecifically, in a case where the coefficient of friction μ is too small(for example, in a case where μ<0.18), interlayer friction between themagnetic surface located on the outermost periphery of the magneticrecording medium 10 which has been already wound around the cartridgereel and the back surface of the magnetic recording medium 10 to benewly wound at its outside becomes extremely low, and the magneticrecording medium 10 to be newly wound can easily deviate from themagnetic surface located on the outermost periphery of the magneticrecording medium 10 which has been already wound. Accordingly, windingdeviation of the magnetic recording medium 10 occurs. On the other hand,in a case where the coefficient of friction μ is too big (for example,in a case where 0.82<μ or 0.80<μ), interlayer friction between the backsurface of the magnetic recording medium 10 to be just wound out fromthe outermost periphery of the reel on the drive side and the magneticsurface of the magnetic recording medium 10 which is located immediatelybelow the former one and still wound around the drive reel becomesextremely high, and the back surface and the magnetic surface areadhered to each other. Accordingly, movement of the magnetic recordingmedium 10 toward the cartridge reel becomes unstable, this causeswinding deviation of the magnetic recording medium 10.

The coefficient of friction μ is determined as follows. Firstly, themagnetic recording medium 10 having a width of ½ inches is wound arounda cylindrical column having a 1 inch diameter with the back surfaceoutward, thereby fixing the magnetic recording medium 10.

Subsequently, with the cylindrical column, the magnetic recording medium10 having a width of ½ inches is brought into contact at a holding angleθ (°)=180°+1 to 180°−10° in such a manner that the magnetic surface isin contact with the column, and one end of the magnetic recording medium10 is connected with a movable strain gauge, and a tension T₀=0.6 (N) isapplied to the other end. The movable strain gauge was shuttled to andfro eight times at 0.5 mm/s, and the readings T₁ (N) to T₈ (N) of thestrain gauge at each outward path were measured, and the average of T₄to T₈ is recorded as T_(ave) (N). Thereafter, the coefficient offriction μ is determined by the following formula.

$\begin{matrix}{\mu = {\frac{1}{( {\theta\lbrack{^\circ}\rbrack} ) \times ( {\pi\text{/}180} )} \times {\log_{e}( \frac{T_{ave}\lbrack N\rbrack}{T_{0}\lbrack N\rbrack} )}}} & \lbrack {{Math}.\mspace{14mu} 5} \rbrack\end{matrix}$

(Surface Roughness R_(ab) of Back Layer)

The surface roughness of the back layer 14 (more specifically, thesurface roughness of the back surface) R_(ab) [nm] is preferably 7.5 nmor less, and more preferably 7.2 nm or less, and even more preferably7.0 nm or less, 6.5 nm or less, 6.3 nm or less, or 6.0 nm or less.Furthermore, the surface roughness R_(ab) is preferably 3.0 nm or more,more preferably 3.2 nm or more, and even more preferably 3.4 nm or more.In a case where the surface roughness R_(ab) of the back layer is withinthe above-described range, the magnetic recording medium 10 has improvedhandleability. Additionally, the influence on the surface of themagnetic layer is reduced during winding of the magnetic recordingmedium 10, and deleterious effect on the electromagnetic conversioncharacteristic is suppressed. The handleability and the electromagneticconversion characteristic are contradictory characteristics, but thesurface roughness R_(ab) within the above-described value range makesthem compatible.

The surface roughness of the back surface R_(ab) is determined asfollows. Firstly, a magnetic recording medium 10 having a width of ½inches is provided, bonded to a slide glass with its back surface upward(more specifically, the magnetic surface is bonded to the slide glass),thus obtaining a sample piece. Subsequently, surface roughness of theback surface of the sample piece is measured using the below-describednoncontact roughness meter using light interference.

Apparatus: noncontact roughness meter using light interference

(noncontact surface-layer sectional shape measuring system, VertScanR5500GL-M100-AC, Ryoka Systems Inc.)

Objective lens: 20 times (field: about 237 μm×178 μm)

Resolution: 640 points×480 points

Measurement mode: phase

Wavelength filter: 520 nm

Surface correction: corrected by secondary multinomial approximationplane

As described above, the surface roughness is measured at least five ormore points in the longitudinal direction, and then the average of eacharithmetic mean roughness Sa (nm), which is automatically calculatedfrom the surface profile obtained at each point, is recorded as thesurface roughness of the back surface R_(ab) (nm).

(Rate of Shrinkage in the Longitudinal Direction) The rate of shrinkageof the magnetic recording medium 10 in the longitudinal direction is0.08% or less, and preferably 0.07% or less. If the rate of shrinkage iswithin the above-described value range, suitability to the use in arecording and reproducing apparatus will not change even if the magneticrecording medium is stored for a long term. Therefore, undesirablephenomena for magnetic recording, such as an off-track phenomenon,hardly occur. The rate of shrinkage in the longitudinal direction maybe, for example, 0% or more.

The rate of shrinkage is determined as follows. Firstly, the magneticrecording medium 10 having a width of ½ inches is provided, cut into apiece having a length of 50 mm, thus making a sample. On the surface ofthe sample on the magnetic layer side, indentations of 15-mm width aremade with a needle at two points in the longitudinal direction, and thedistance L1 (mm) between the two points is measured using TOPCONTUM-220ES and CORDINATE COMPUTER CA-1B. Subsequently, the sample isstored for 72 hours in a dry thermostat bath at 60° C. with no tensionapplied. Subsequently, the sample is taken out from the thermostat bath,allowed to stand at room temperature for one hour, and then the distanceL2 (mm) between the two points on the sample is measured in the samemanner as for L1. Thereafter, the rate of shrinkage is determined by thefollowing formula.Rate of shrinkage (%)=((L1−L2)/L1)×100

As described above, three piece of samples of 50-mm length are cut outfrom a tape of 1 m at almost equal distances, the three samples aresubjected to similar measurement, and the average of the rate ofshrinkage (%) of these samples are recorded as the rate of shrinkage (%)in the longitudinal direction.

The rate of shrinkage may be, for example, adjusted as follows. In orderto suppress shrinkage in the magnetic recording medium 10, for example,the base tension may be adjusted in the application process or dryingprocess of the magnetic recording medium 10, or the winding tension maybe adjusted in the application process. Additionally, in order to relaxshrinkage generated in the magnetic recording medium 10, for example,the magnetic recording medium 10 may be stored in a cartridge for oneweek in an environment at 50° C. and 50% Rh, or the magnetic recordingmedium 10 may be stored at 60° C. for three days in the productionprocess after the curing process.

(1% Elongation Load in the Longitudinal Direction)

The 1% elongation load of the magnetic recording medium 10 in thelongitudinal direction is preferably 0.60 N or less, more preferably0.55 N or less, and more preferably 0.52 N or less. The 1% elongationload is preferably 0.20 N or more, more preferably 0.30 N or more, andeven more preferably 0.40 N or more. If the 1% elongation load is withinthe above-described value range, suitability to the use in a recordingand reproducing apparatus is improved.

The 1% elongation load is determined as follows. Firstly, a magneticrecording medium 10 having a width of ½ inches is provided, cut into apiece having a length of 100 mm, thus making a sample. The sample ispulled at a room temperature with AUTOGRAPH AG-100D (ShimadzuCorporation) at a pulling speed of 10 mm/min under a 0.5% elongationload (σ0.5) and a 1.5% elongation load (σ1.5), and the values ofσ1.5-σ0.5 are recorded as the 1% elongation load (N).

(Coercivity Hc)

The coercivity He of the magnetic recording medium 10 measured in thethickness direction (vertical direction) is preferably 220 kA/m or moreand 310 kA/m or less, more preferably 230 kA/m or more and 300 kA/m orless, and even more preferably 240 kA/m or more and 290 kA/m or less. Ifthe coercivity He is 220 kA/m or more, the coercivity He is sufficientand thus deterioration of a magnetization signal recorded on theadjacent tracks caused by a leaked magnetic field from the recordinghead is suppressed. Accordingly, better SNR is obtained.

On the other hand, if the coercivity He is 310 kA/m or less, saturatedrecording with a recording head is facilitated, so that better SNR isobtained.

The coercivity He is determined as follows. Firstly, a measurementsample is cut out from the long magnetic recording medium 10, and theM-H loop of the entire measurement sample is measured using a vibratingsample magnetometer (VSM) in the thickness direction of the measurementsample (the thickness direction of the magnetic recording medium 10).Subsequently, the coating films (for example, the primary layer 12 andthe magnetic layer 13) are removed using acetone or ethanol, the baselayer 11 was left alone for background correction, and the M-H loop ofthe base layer 11 is measured in the thickness direction of the baselayer 11 (the thickness direction of the magnetic recording medium 10)using VSM. Thereafter, the M-H loop of the base layer 11 is subtractedfrom the M-H loop of the entire measurement sample, and the M-H loopafter background correction is obtained. The coercivity He is determinedfrom the M-H loop thus obtained. Note that the measurements of the M-Hloop are carried out at 25° C. In addition, the “diamagnetic fieldcorrection” in the measurement of the M-H loop in the vertical directionof the magnetic recording medium 10 is not carried out.

(Ratio R Between Coercivity Hc(50) and Coercivity Hc(25))

The ratio R between the coercivity Hc(50) of the magnetic recordingmedium 10 measured at 50° C. in the thickness direction (verticaldirection) and the coercivity Hc(25) of the magnetic recording medium 10measured at 25° C. in the thickness direction (=(Hc(50)/Hc(25))×100) ispreferably 95% or more, more preferably 96% or more, even morepreferably 97% or more, and particularly preferably 98% or more. If theproportion R is 95% or more, temperature dependency of the coercivity Hedecreases, and deterioration of SNR in high temperature environments issuppressed.

The coercivity Hc(25) is determined in a manner similar to the methodfor measuring the coercivity Hc. In addition, the coercivity Hc(50) isdetermined in a manner similar to the method for measuring thecoercivity Hc, except that the M-H loops of the measurement sample andthe base layer 11 are measured at 50° C.

(Squareness Ratio S1 Measured in the Longitudinal Direction)

The squareness ratio S1 of the magnetic recording medium 10 measured inthe longitudinal direction (traveling direction) is preferably 35% orless, more preferably 27% or less, and even more preferably 20% or less.If the squareness ratio S1 is 35% or less, the magnetic powder hassufficiently high vertical orientation, so that better SNR is obtained.Accordingly, better electromagnetic conversion characteristic isobtained. Additionally, the shape of a servo signal is improved, andcontrol on the drive side is more facilitated.

In the present description, vertical orientation of the magneticrecording medium can mean that the squareness ratio S1 of the magneticrecording medium is within the above-described value range (for example,35% or less). The magnetic recording medium according to the presenttechnology is preferably vertically oriented.

The squareness ratio S1 is determined as follows. Firstly, a measurementsample is cutout from the long magnetic recording medium 10, and the M-Hloop of the entire measurement sample corresponding to the longitudinaldirection (traveling direction) of the magnetic recording medium 10 ismeasured using VSM. Subsequently, the coating films (for example, theprimary layer 12 and the magnetic layer 13) are removed using, forexample, acetone or ethanol, the base layer 11 is left alone forbackground correction, and the M-H loop of the base layer 11corresponding to the longitudinal direction of the base layer 11(traveling direction of the magnetic recording medium 10) is measuredusing VSM. Thereafter, the M-H loop of the base layer 11 is subtractedfrom the M-H loop of the entire measurement sample, thus obtaining theM-H loop after background correction. The magnetization saturation Ms(emu) of the M-H loop thus obtained and the residual magnetization Mr(emu) are substituted into the following formula, thereby calculatingthe squareness ratio S1 (%). Note that the measurement of the M-H loopis carried out at 25° C.Squareness ratio S1(%)=(Mr/Ms)×100

(Squareness Ratio S2 Measured in the Vertical Direction)

The squareness ratio S2 of the magnetic recording medium 10 measured inthe vertical direction (thickness direction) is preferably 65% or more,more preferably 73% or more, and even more preferably 80% or more. Ifthe squareness ratio S2 is 65% or more, the magnetic powder hassufficiently high vertical orientation, so that better SNR is obtained.Accordingly, better electromagnetic conversion characteristic isobtained. Additionally, the servo signal shape is improved, control onthe drive side is facilitated.

In the present description, vertical orientation of the magneticrecording medium may mean that the squareness ratio S2 of the magneticrecording medium is within the above-described value range (for example,65% or more).

The squareness ratio S2 is determined in a manner similar to thedetermination of the squareness ratio S1, except that the M-H loop ismeasured in the vertical direction (thickness direction) of the magneticrecording medium 10 and the base layer 11. Note that, in the measurementof the squareness ratio S2, “diamagnetic field correction” in themeasurement of the M-H loop in the vertical direction of the magneticrecording medium 10 is not carried out.

The squareness ratios S and S2 are set at desired values by adjusting,for example, the intensity of a magnetic field applied to the magneticlayer forming paint, the time for application of a magnetic field to themagnetic layer forming paint, the dispersion condition of a magneticpowder in the magnetic layer forming paint, or the concentration of thesolid component in the magnetic layer forming paint. Specifically, forexample, with the increase of the intensity of a magnetic field, thesquareness ratio S1 decreases, while the squareness ratio S2 increases.Additionally, with the increase of the time for application of amagnetic field, the squareness ratio S1 decreases, while the squarenessratio S2 increases. Additionally, with the improvement of the dispersioncondition of a magnetic powder, the squareness ratio S1 decreases, whilethe squareness ratio S2 increases. Additionally, with the decrease ofthe concentration of the solid component, the squareness ratio S1decreases, while the squareness ratio S2 increases. Note that theadjustment method may be used alone, or in combination of two or more ofthem.

(SFD)

In the switching field distribution (SFD) curve of the magneticrecording medium 10, the peak ratio X/Y of the height X of the main peakand the height Y of the sub peak in the vicinity of the zero magneticfield is preferably 3.0 or more, more preferably 5.0 or more, even morepreferably 7.0 or more, particularly preferably 10.0 or more, and mostpreferably 20.0 or more (see FIG. 4). If the peak ratio X/Y is 3.0 ormore, inclusion of large amounts of low coercivity components (forexample, soft magnetic particles and super paramagnetic particles)characteristic to ε-iron oxide in the magnetic powder besides the ε-ironoxide particles contributing to actual recording is suppressed.Accordingly, this suppresses deterioration of a magnetizing signalrecorded on the adjacent track by a magnetic field leaked from arecording head, whereby better SNR is obtained. The upper limit of thepeak ratio X/Y is not particularly limited, and, for example, 100 orless.

The peak ratio X/Y is determined as follows. Firstly, in a mannersimilar to the measurement of the coercivity Hc, the M-H loop afterbackground correction is obtained. Subsequently, a SFD curve is obtainedfrom the M-H loop thus obtained. Calculation of the SFD curve may use aprogram attached to the measuring instrument, or other program. Theabsolute value of the point where the calculated SFD curve traverses theY axis (dM/dH) is defined as “Y”, and the height of the main peakobserved near the coercivity He in the M-H loop is defined as “X”, andthe peak ratio X/Y is calculated. Note that measurement of the M-H loopis carried out at 25° C. in a manner similar to the method for measuringthe coercivity Hc. Additionally, the “diamagnetic field correction” inthe measurement of the M-H loop in the thickness direction (verticaldirection) of the magnetic recording medium 10 is not carried out.

(Activated volume V_(act)) The activated volume V_(act) is preferably8000 nm³ or less, more preferably 6000 nm³ or less, even more preferably5000 nm³ or less, particularly preferably 4000 nm³ or less, and mostpreferably 3000 nm³ or less. If the activated volume V_(act) is 8000 nm³or less, dispersion condition of the magnetic powder is good, so thatthe bit inversion region can be steepened, and this suppressesdeterioration of a magnetization signal recorded on the adjacent trackscaused by leakage of a magnetic field from the recording head.Accordingly, better SNR may be obtained.

The activated volume V_(act) is determined by the following formuladerived by Street & Woolley.V _(act) (nm³)=k _(B) ×T×X _(irr)/(μ₀ ×Ms×S)

(Note that k_(B): Boltzmann constant (1.38×10⁻²³ J/K), T: temperature(K), X_(irr): nonreversible magnetic susceptibility, μ₀: vacuum magneticpermeability, S: coefficient of magnetic viscosity,

Ms: magnetization saturation (emu/cm³))

The nonreversible magnetic susceptibility X_(irr), the magnetizationsaturation Ms, and the coefficient of magnetic viscosity S substitutedinto the above formula are determined as follows using VSM. Note thatthe measurement direction by VSM is the thickness direction (verticaldirection) of the magnetic recording medium 10. Additionally themeasurement by VSM is carried out at 25° C. on a measurement sample cutout from the long magnetic recording medium 10. Additionally, the“diamagnetic field correction” in the measurement of the M-H loop in thethickness direction (vertical direction) of the magnetic recordingmedium 10 is not carried out.

(Nonreversible Magnetic Susceptibility X^(irr))

The nonreversible magnetic susceptibility X_(irr) is defined as thedecline near the residual coercivity Hr in the decline of the residualmagnetization curve (DCD curve). Firstly, a magnetic field of −1193 kA/m(15 kOe) is applied to the whole of the magnetic recording medium 10,and the magnetic field is returned to zero thereby making a residualmagnetization state. Thereafter, a magnetic field of about 15.9 kA/m(200 Oe) is applied in the opposite direction and the magnetic field isreturned to zero again, and the residual magnetization amount ismeasured. Thereafter, in a similar way, a magnetic field which is 15.9kA/m larger than the previously applied magnetic field is applied andthe magnetic field is returned to zero, this measurement is repeatedlycarried out, and the residual magnetization amount is plotted withreference to the applied magnetic field, thereby measuring the DCDcurve. From the DCD curve thus obtained, the point having a zeromagnetization amount is set as the residual coercivity Hr, additionallythe DCD curve is differentiated, and the decline of the DCD curve ineach magnetic field is determined. In the decline of the DCD curve, thedecline near the residual coercivity Hr is set at X_(irr).

(Magnetization Saturation Ms)

Firstly, the M-H loop of the entire magnetic recording medium 10(measurement sample) is measured in the thickness direction of themagnetic recording medium 10. Subsequently, the coating films (forexample, the primary layer 12 and the magnetic layer 13) are removedusing, for example, acetone and ethanol, and the base layer 11 is leftalone for background correction, and the M-H loop of the base layer 11is measured in the thickness direction in a similar manner. Thereafter,the M-H loop of the base layer 11 is subtracted from the M-H loop of theentire magnetic recording medium 10, thereby obtaining the M-H loopafter background correction. From the value of the magnetizationsaturation Ms (emu) of the M-H loop thus obtained and the volume (cm³)of the magnetic layer 13 in the measurement sample, Ms (emu/cm³) iscalculated. Note that the volume of the magnetic layer 13 can bedetermined by multiplying the area of the measurement sample with theaverage thickness of the magnetic layer 13. The method for calculatingthe average thickness of the magnetic layer 13 necessary for calculatingthe volume of the magnetic layer 13 is described below.

(Coefficient of Magnetic Viscosity S)

Firstly, a magnetic field of −1193 kA/m (15 kOe) is applied to theentire magnetic recording medium 10 (measurement sample), the magneticfield is returned to zero, and the sample is brought into a residualmagnetization state. Thereafter, in the opposite direction, a magneticfield equivalent to the value of the residual coercivity Hr obtained bythe DCD curve is applied. With the magnetic field applied, themagnetization amount is continuously measured at regular time intervalsfor 1000 seconds. The relationship between the time t and themagnetization amount M(t) thus obtained is referred to the followingformula, and the coefficient of magnetic viscosity S is calculated.M(t)=M0+S=ln(t)

(Noted that M(t): magnetization amount at time t, M0: initialmagnetization amount, S: coefficient of magnetic viscosity, ln(t):natural logarithm of time)

(Arithmetic Average Roughness Ra)

The arithmetic average roughness Ra of the magnetic surface ispreferably 2.5 nm or less, and more preferably 2.0 nm or less. If the Rais 2.5 nm or less, better SNR is obtained.

The arithmetic average roughness Ra is determined as follows. Firstly,using an atomic force microscope (AFM) (Dimension Icon, BrukerCorporation), the surface on the side having the magnetic layer 13 isobserved, and a cross section profile is obtained. Subsequently, fromthe cross section profile thus obtained, the arithmetic averageroughness Ra is obtained in accordance with JIS B0601:2001.

(4) Method for Producing Magnetic Recording Medium

Subsequently, the method for producing the magnetic recording medium 10composing the above-described configuration is described. Firstly, anon-magnetic powder, a binder, and others are kneaded with and/ordispersed in a solvent, thereby preparing a primary layer forming paint.Subsequently, a magnetic powder, a binder, and others are kneaded withand/or dispersed in a solvent, thereby preparing a magnetic layerforming paint. Preparation of the magnetic layer forming paint and theprimary layer forming paint may use for example, any of the followingsolvents, dispersers, and kneaders.

Examples of the solvent used for preparation of the paints includeketone solvents such as acetone, methyl ethyl ketone, methyl isobutylketone, and cyclohexanone; alcohol solvents such as methanol, ethanol,and propanol; ester solvents such as methyl acetate, ethyl acetate,butyl acetate, propyl acetate, ethyl lactate, and ethylene glycolacetate; ether solvents such as diethyleneglycol dimethyl ether,2-ethoxyethanol, tetrahydrofuran, and dioxane; aromatic hydrocarbonsolvents such as benzene, toluene, and xylene; and hydrocarbon halidesolvents such as methylene chloride, ethylene chloride, carbontetrachloride, chloroform, and chlorobenzene. These solvents may be usedalone, or in combination of two or more of them. Examples of the kneaderused for the preparation of the paints include, but not particularlylimited to, kneaders such as a continuous biaxial kneading machine, acontinuous biaxial kneading machine allowing multistage dilution, akneader, a pressurizing kneader, and a roll kneader. Additionally,examples of the disperser used for the preparation of the paintsinclude, but not particularly limited to, disperses such as a roll mill,a ball mill, a horizontal sand mill, a vertical sand mill, a spike mill,a pin mill, a tower mill, a pearl mill (for example, “DCP mill”, EinrichDraiswerkes), a homogenizer, and an ultrasonic disperser.

Subsequently, the primary layer forming paint is applied to one of themain surfaces of the base layer 11 and dried, thereby forming theprimary layer 12. Subsequently, the magnetic layer forming paint isapplied to the primary layer 12 and dried, thereby forming the magneticlayer 13 on the primary layer 12. Note that, in the drying process, amagnetic powder is subjected to magnetic field orientation in thethickness direction of the base layer 11 using, for example, a solenoidcoil. Alternatively, in the drying process, a magnetic powder issubjected to magnetic field orientation in the longitudinal direction(traveling direction) of the base layer 11 using, for example, asolenoid coil, and then subjected to magnetic field orientation in thethickness direction of the base layer 11. After formation of themagnetic layer 13, the back layer 14 is formed on the other main surfaceof the base layer 11. As a result of this, the magnetic recording medium10 is obtained.

Thereafter, the magnetic recording medium 10 thus obtained is woundagain around a large diameter core, and subjected to curing treatment.Finally, the magnetic recording medium 10 is calendared, and cut to apredetermined width (for example, a width of ½ inches). In this manner,the desired slim and long magnetic recording medium 10 is obtained.

(5) Recording and Reproducing Apparatus

[Configuration of Recording and Reproducing Apparatus]

Subsequently, an example of the configuration of a recording andreproducing apparatus 30 for recording and reproducing the magneticrecording medium 10 having the above-described configuration isdescribed with reference to FIG. 5.

The recording and reproducing apparatus 30 has a configuration allowingadjustment of the tension applied to the magnetic recording medium 10 inthe longitudinal direction. Additionally, the recording and reproducingapparatus 30 has a configuration allowing loading of a magneticrecording medium cartridge 10A. For easy understanding, the recordingand reproducing apparatus 30 referred to herein has a configurationwhich can load one magnetic recording medium cartridge 10A, but therecording and reproducing apparatus 30 may have a configuration whichcan load a plurality of magnetic recording medium cartridges 10A.

The recording and reproducing apparatus 30 is connected to informationprocessors such as a server 41 and a personal computer (hereinafterreferred to as “PC”) 42 through a network 43, and is configured to allowrecording of the data supplied from these information processors on themagnetic recording medium cartridge 10A. The shortest recordingwavelength of the recording and reproducing apparatus 30 is preferably100 nm or less, more preferably 75 nm or less, even more preferably 60nm or less, and particularly preferably 50 nm or less.

The recording and reproducing apparatus includes, as depicted in FIG. 5,a spindle 31, a reel 32 on the recording and reproducing apparatus side,a spindle driving apparatus 33, a reel driving apparatus 34, a pluralityof guide rollers 35, a head unit 36, a communication interface(hereinafter referred to as I/F) 37, and a controller 38.

The spindle 31 is configured to allow loading of the magnetic recordingmedium cartridge 10A. The magnetic recording medium cartridge 10A is inconformity with Linear Tape Open (LTO) specification, and is containedin the cartridge case 10B so as to allow rotation of a single reel 10Cwound with the magnetic recording medium 10. On the magnetic recordingmedium 10, a servo pattern in an inverted V shape as a servo signal hasbeen recorded. The reel 32 is configured so as to allow fixation of thetip of the magnetic recording medium 10 drawn from the magneticrecording medium cartridge 10A.

The present technology also provides a magnetic recording cartridgeincluding a magnetic recording medium according to the presenttechnology. In the magnetic recording cartridge, the magnetic recordingmedium may be, for example, wound around a reel.

The spindle driving apparatus 33 is an apparatus for rotating anddriving the spindle 31. The reel driving apparatus 34 is an apparatusfor rotating and driving the reel 32. In a case where data is recordedor reproduced on the magnetic recording medium 10, the spindle drivingapparatus 33 and the reel driving apparatus 34 rotate and drive thespindle 31 and the reel 32 to travel the magnetic recording medium 10.The guide roller 35 is a roller for guiding the traveling of themagnetic recording medium 10.

The head unit 36 includes a plurality of recording heads for recording adata signal on the magnetic recording medium 10, a plurality ofreproducing heads for reproducing the data signal recorded on themagnetic recording medium 10, and a plurality of servo heads forreproducing the servo signal recorded on the magnetic recording medium10. The recording head may be, for example, a ring-shaped head, but thetype of the recording head is not limited to this.

The communication I/F 37 communicates with the information processorssuch as the server 41 and the PC 42, and is connected to the network 43.

The controller 38 controls the entire recording and reproducingapparatus 30. For example, according to requests of the informationprocessors such as the server 41 and the PC 42, the controller 38records the data signal supplied from the information processors on themagnetic recording medium 10 by the head unit 36. Additionally,according to requests of the information processors such as the server41 and the PC 42, the controller 38 reproduces the data signal recordedon the magnetic recording medium 10 by the head unit 36, and suppliesthe data signal to the information processors.

Additionally, on the basis of the servo signal supplied from the headunit 36, the controller 38 detects width change of the magneticrecording medium 10. Specifically, as the servo signal, a plurality ofservo patterns in an inverted V shape is recorded on the magneticrecording medium 10, the head unit 36 reproduces different two servopatterns simultaneously with the two servo heads on the head unit 36,thus obtaining each servo signal. Using the relative positionalinformation of the servo patterns and the head unit obtained from theservo signal, the position of the head unit 36 is controlled so as tofollow the servo pattern. At the same time, information regarding thedistance between the servo patterns is also obtained by comparing thetwo servo signal waveforms. Changes in the distance between the servopatterns in these measurements can be obtained by comparing theinformation regarding the distance between the servo patterns obtainedin these measurements. The width change of the magnetic recording medium10 can be also calculated by adding the information regarding thedistance between the servo patterns in servo pattern recording to thechanges in the distance between the servo patterns. On the basis of thechange in the distance between the servo patterns obtained as describedabove, or the change of the calculated width of the magnetic recordingmedium 10, the controller 38 controls rotation and driving of thespindle driving apparatus 33 and the reel driving apparatus 34, andadjusts the tension of the magnetic recording medium 10 in thelongitudinal direction so as to make the width of the magnetic recordingmedium 10 the predetermined width or almost the predetermined width. Asa result of this, width change of the magnetic recording medium 10 issuppressed.

[Operation of Recording and Reproducing Apparatus]

Subsequently, operation of the recording and reproducing apparatus 30having the above-described configuration is described.

Firstly, the magnetic recording medium cartridge 10A is mounted on therecording and reproducing apparatus 30, the leading end of the magneticrecording medium 10 is pulled out, and transferred to the reel 32through a plurality of the guide rollers 35 and the head units 36, andthe leading edge of the magnetic recording medium 10 is attached to thereel 32.

Subsequently, by operating an operating unit (not depicted), the spindledriving apparatus 33 and the reel driving apparatus 34 are driven bycontrol of the controller 38, and the spindle 31 and the reel 32 arerotated in the same direction so as to travel the magnetic recordingmedium 10 from the reel 10C toward the reel 32. As a result of this,while the magnetic recording medium 10 is wound around the reel 32, thehead unit 36 records information on the magnetic recording medium 10 orreproduces information recorded on the magnetic recording medium 10.

Additionally, in a case where the magnetic recording medium 10 rewoundaround the reel 10C, the spindle 31 and the reel 32 are rotatably drivenin a direction opposite to the above-described direction, whereby themagnetic recording medium 10 is traveled from the reel 32 to the reel10C. Also in this rewinding, recording of information on the magneticrecording medium 10 or reproduction of information recorded on themagnetic recording medium 10 is carried out by the head unit 36.

(6) Effect

In the magnetic recording medium 10 according to the first embodiment,the average thickness t_(T) of the magnetic recording medium 10 ist_(T)≤5.5 μm, the dimensional variation Δw of the magnetic recordingmedium 10 in the width direction to the tension change of the magneticrecording medium 10 in the longitudinal direction is 650 ppm/N≤Δw, andthe rate of shrinkage in the longitudinal direction is 0.08% or less. Asa result of this, width change of the magnetic recording medium 10 canbe suppressed by adjusting the tension of the magnetic recording medium10 in the longitudinal direction using a recording and reproducingapparatus. For example, even if temperature and humidity change, whichcan cause width change of the magnetic recording medium 10, occurs, thewidth of the magnetic recording medium 10 is kept constant or generallyconstant. The suppression of the width change through the tensionadjustment is possible even after long-term storage. Furthermore, themagnetic recording medium 10 is as thin as t_(T)≤5.5 μm, but has markedhandleability.

(7) Modification

[Modification 1]

As depicted in FIG. 7, the magnetic recording medium 10 may furtherinclude a barrier layer 15 provided on at least one surface of the baselayer 11. The barrier layer 15 is a layer for suppressing dimensionalchange of the base layer 11 according to environment. For example, anexample of the factor causing the dimensional change is hygroscopicityof the base layer 11, and the barrier layer 15 reduces the rate ofinvasion of moisture into the base layer 11. The barrier layer 15includes a metal or a metal oxide. The metal may be, for example, atleast one of Al, Cu, Co, Mg, Si, Ti, V, Cr, Mn, Fe, Ni, Zn, Ga, Ge, Y,Zr, Mo, Ru, Pd, Ag, Ba, Pt, Au, or Ta. The metal oxide may be, forexample, at least one of Al₂O₃, CuO, CoO, SiO₂, Cr₂O₃, TiO₂, Ta₂O₅, orZrO₂, or any of the oxide of the metal listed above. Alternatively,diamond-like carbon (DLC) or diamond may be used.

The average thickness of the barrier layer 15 is preferably 20 nm ormore and 1000 nm or less, and more preferably 50 nm or more and 1000 nmor less. The average thickness of the barrier layer 15 is determined ina manner similar to the average thickness t_(m) of the magnetic layer13. However, the magnification of the TEM image is adjusted asappropriate according to the thickness of the barrier layer 15.

[Modification 2]

The magnetic recording medium 10 may be incorporated into a libraryapparatus. More specifically, the present technology also provides alibrary apparatus including at least one magnetic recording medium 10.The library apparatus has a configuration which can adjust the tensionapplied to the magnetic recording medium 10 in the longitudinaldirection, and may include a plurality of the recording and reproducingapparatuses 30.

[Modification 3]

The magnetic recording medium 10 may be subjected to servo signalwrite-in processing by a servo writer. By adjustment of the tension ofthe magnetic recording medium 10 in the longitudinal direction by theservo writer during, for example, recording of a servo signal, the widthof the magnetic recording medium 10 can be kept constant or generallyconstant. In this case, the servo writer may include a detectionapparatus for detecting the width of the magnetic recording medium 10.The servo writer can adjust the tension of the magnetic recording medium10 in the longitudinal direction on the basis of the detection result ofthe detection apparatus.

3. SECOND EMBODIMENT (EXAMPLE OF MAGNETIC RECORDING MEDIUM OF VACUUMTHIN FILM TYPE) (1) Configuration of Magnetic Recording Medium

The magnetic recording medium 110 according to the second embodiment isa long vertical magnetic recording medium, and includes, as depicted inFIG. 8, a filmy base layer 111, a soft magnetic underlayer (hereinafterreferred to as “SUL”) 112, a first seed layer 113A, a second seed layer113B, a first primary layer 114A, a second primary layer 114B, and amagnetic layer 115. The SUL 112, the first and second seed layers 113Aand 113B, the first and second primary layers 114A and 114B, and themagnetic layer 115 may be, for example, vacuum thin films such as alayer formed by sputtering (hereinafter may be referred to as“sputtering layer”). The SUL 112, the first and second seed layers 113Aand 113B, and the first and second primary layers 114A and 114B areprovided between one main surface of the base layer 111 (hereinafterreferred to as “surface”) and the magnetic layer 115, and the SUL 112,the first seed layer 113A, the second seed layer 113B, the first primarylayer 114A, and the second primary layer 114B are laminated in thisorder from the base layer 111 toward the magnetic layer 115.

The magnetic recording medium 110 may include, as necessary, aprotective layer 116 provided on the magnetic layer 115 and alubricating layer 117 provided on the protective layer 116.Additionally, the magnetic recording medium 110 may further include, asnecessary, a back layer 118 provided on the other main surface of thebase layer 111 (hereinafter referred to as “back surface”).

Hereinafter the longitudinal direction of the magnetic recording medium110 (the longitudinal direction of the base layer 111) is referred to asmachine direction (MD). Here, the machine direction is the movingdirection of the recording and reproducing head relative to the magneticrecording medium 110, more specifically the traveling direction of themagnetic recording medium 110 during recording and reproducing.

The magnetic recording medium 110 according to the second embodiment issuitable as a storage media for data archive, the demand for which isexpected to further grow in future. The magnetic recording medium 110can achieve, for example, ten times or more the surface recordingdensity of the current storage magnetic recording medium of coatingtype, or 50 Gb/in² or more of the surface recording density. In a casewhere a data cartridge of common linear recording system is composedusing the magnetic recording medium 110 having such surface recordingdensity, high-capacity recording of 100 TB or more per one datacartridge will be achieved.

The magnetic recording medium 110 according to the second embodiment issuitable for the use in a recording and reproducing apparatus (recordingand reproducing apparatus for recording and reproducing data) having aring-shaped recording head and a reproducing head of giantmagnetoresistive (GMR) type or tunneling magnetoresistive (TMR) type.Additionally, for the magnetic recording medium 110 according to thesecond embodiment, the use of a ring-shaped recording head as a servosignal writing head is preferred. On the magnetic layer 115, forexample, a data signal is vertically recorded with a ring-shapedrecording head. Additionally, on the magnetic layer 115, for example, aservo signal is vertically recorded with a ring-shaped recording head.

(2) Details of Each Layer

(Base Layer)

For the base layer 111, the description about the base layer 11 in thefirst embodiment holds true, so that description about the base layer111 is omitted.

(SUL)

The SUL 112 includes an amorphous soft magnetic material. The softmagnetic material includes, for example, at least one of Co materials orFe materials. Examples of the Co material include CoZrNb, CoZrTa, orCoZrTaNb. Examples of the Fe material include FeCoB, FeCoZr, or FeCoTa.

The SUL 112 is a single layer SUL, and is directly provided on the baselayer 111. The average thickness of the SUL 112 is preferably 10 nm ormore and 50 nm or less, and more preferably 20 nm or more and 30 nm orless.

The average thickness of the SUL 112 is determined by the same method asthat for measuring the average thickness of the magnetic layer 13 in thefirst embodiment. Note that the average thickness of the below-describedlayers other than the SUL 112 (more specifically, the averagethicknesses of the first and second seed layers 113A and 113B, the firstand second primary layers 114A and 114B, and the magnetic layer 115) canbe determined by the same method as the method for measuring the averagethickness of the magnetic layer 13 in the first embodiment. However, themagnification of the TEM image is adjusted as appropriate according tothe thickness of each layer.

(First and Second Seed Layers)

The first seed layer 113A includes an alloy including Ti and Cr, and hasan amorphous state. In addition, the alloy may further include O(oxygen). The oxygen may be impurity oxygen included in a trace amountin the first seed layer 113A during formation of the first seed layer113A by a deposition method such as a sputtering method.

The term “alloy” means at least one of, for example, a solid solution,an eutectic body, or an intermetallic compound containing Ti and Cr. Theterm “amorphous state” means that halo is observed by, for example,X-ray diffraction or electron diffraction, and no crystal structure canbe specified.

The atomic ratio of Ti to the total amount of Ti and Cr included in thefirst seed layer 113A is preferably 30 atom % or more and less than 100atom %, and more preferably 50 atom % or more and less than 100 atom %.If the atomic ratio of Ti is less than 30%, the (100) face of thebody-centered cubic lattice (bcc) structure of Cr is oriented, wherebyorientation of the first and second primary layers 114A and 114B formedon the first seed layer 113A may decrease.

The atomic ratio of Ti is determined as follows. While subjecting themagnetic recording medium 110 to ion milling from the side of themagnetic layer 115, depth profile analysis of the first seed layer 113Ais carried out by Auger electron spectroscopy (hereinafter referred toas “AES”). Subsequently, the average compositions (average atomicratios) of Ti and Cr in the film thickness direction are determined fromthe depth profile thus obtained. Subsequently, using the determinedaverage compositions of Ti and Cr, the atomic ratio of Ti is determined.

In a case where the first seed layer 113A includes Ti, Cr, and O, theatomic ratio of O to the total amount of Ti, Cr, and O included in thefirst seed layer 113A is preferably 15 atom % or less, and morepreferably 10 atom % or less. If the atomic ratio of O is more than 15atom %, TiO₂ crystal is generated to influence the nucleation of thefirst and second primary layers 114A and 114B formed on the first seedlayer 113A, and orientation of the first and second primary layers 114Aand 114B may decrease. The atomic ratio of the O is determined using ananalysis method similar to that for the atomic ratio of the Ti.

The alloy included in the first seed layer 113A may further includeother additional element besides Ti and Cr. Examples of the additionalelement include at least one element selected from the group includingNb, Ni, Mo, Al, and W.

The average thickness of the first seed layer 113A is preferably 2 nm ormore and 15 nm or less, and more preferably 3 nm or more and 10 nm orless.

The second seed layer 113B includes, for example, NiW or Ta, and has acrystalline state. The average thickness of the second seed layer 113Bis preferably 3 nm or more and 20 nm or less, and more preferably 5 nmor more and 15 nm or less.

The first and second seed layers 113A and 113B have a crystal structuresimilar to that of the first and second primary layers 114A and 114B,and are not seed layers provided for the purpose of crystal growth, butare seed layers improving vertical orientation of the first and secondprimary layers 114A and 114B by the amorphous state of the first andsecond seed layers 113A and 113B.

(First and Second Primary Layers)

The first and second primary layers 114A and 114B preferably have acrystal structure similar to that of the magnetic layer 115. In a casewhere the magnetic layer 115 includes a Co alloy, the first and secondprimary layers 114A and 114B preferably include a material having ahexagonal close-packed (hcp) structure similar to that of a Co alloy,and the c axis of the structure is preferably oriented in a verticaldirection (more specifically in a film thickness direction) to the filmsurface. This improves orientation of the magnetic layer 115, andachieves relatively good matching of the lattice constants of the secondprimary layer 114B and the magnetic layer 115. The material having ahexagonal close-packed (hcp) structure is preferably a materialincluding Ru, and specifically preferably simple Ru or a Ru alloy.Examples of the Ru alloy include Ru alloy oxides such as Ru—SiO₂,Ru—TiO₂, and Ru—ZrO₂, and the Ru alloy may be one of them. As describedabove, a similar material may be used as the materials of the first andsecond primary layers 114A and 114B. However, the intended effect of thefirst and second primary layers 114A and 114B are different.Specifically, the second primary layer 114B has a layer structure whichpromotes the granular structure of the magnetic layer 115 as the upperlayer, and the first primary layer 114A has a layer structure havinghigh crystal orientation. In order to obtain these layer structures,deposition conditions such as sputtering conditions for the first andsecond primary layers 114A and 114B are preferably different.

The average thickness of the first primary layer 114A is preferably 3 nmor more and 15 nm or less, and more preferably 5 nm or more and 10 nm orless. The average thickness of the second primary layer 114B ispreferably 7 nm or more and 40 nm or less, and more preferably 10 nm ormore and 25 nm or less.

(Magnetic Layer)

The magnetic layer (may be referred to as recording layer) 115 may be avertical magnetic recording layer including a vertically orientedmagnetic material. The magnetic layer 115 is preferably a granularmagnetic layer including a Co alloy, from the viewpoint of improving itsrecording density. The granular magnetic layer includes ferromagneticcrystal particles including a Co alloy, and non-magnetic grainboundaries (non-magnetic substance) surrounding the ferromagneticcrystal particles. More specifically, the granular magnetic layerincludes columns (columnar crystals) including a Co alloy andnon-magnetic grain boundaries (for example, oxide such as SiO₂)surrounding the columns and magnetically separate these columns. Thisstructure composes the magnetic layer 115 having a structure includingmagnetically separated columns.

The Co alloy has a hexagonal close-packed (hcp) structure, and its caxis is oriented in a vertical direction (film thickness direction)relative to the film surface. As the Co alloy, it is preferred that aCoCrPt alloy including at least Co, Cr, and Pt be used. The CoCrPt alloymay further include an additional element. Examples of the additionalelement include at least one element selected from the group includingNi, Ta, and the like.

The non-magnetic grain boundaries surrounding the ferromagnetic crystalparticles include a non-magnetic metal material. The metal includessemimetals. As the non-magnetic metal material, for example, at leastone of metal oxide or metal nitride may be used, and the use of metaloxide is preferred, from the viewpoint of stably keeping a granularstructure. Examples of the metal oxide include metal oxides containingat least one element selected from the group including Si, Cr, Co, Al,Ti, Ta, Zr, Ce, Y, Hf, and the like, and metal oxides including at leastSi oxide (more specifically, SiO₂) is preferred. Specific examples ofthe metal oxide include SiO₂, Cr₂O₃, CoO, Al₂O₃, TiO₂, Ta₂O₅, ZrO₂, andHfO₂. Examples of the metal nitride include metal nitrides containing atleast one element selected from the group including Si, Cr, Co, Al, Ti,Ta, Zr, Ce, Y, Hf, and the like. Specific examples of the metal nitrideinclude SiN, TiN, and AlN. The CoCrPt alloy included in theferromagnetic crystal particles and the S1 oxide included in thenon-magnetic grain boundaries preferably have the average compositionrepresented by the following formula (1). The reason for this is that amagnetization saturation Ms which suppresses the influence of ademagnetizing field and ensures sufficient reproduction output isachieved, whereby further improvement of recording and reproducingcharacteristic is achieved.(Co_(x)Pt_(y)Cr_(100-x-y))_(100-z)—(SiO₂)_(z)  (1)

(Note that in the formula (1), x, y, and z are the values within theranges of 69≤x≤75, 10≤y≤16, and 9≤z≤12, respectively.)

Note that the above composition can be determined as follows. Whilesubjecting the magnetic recording medium 110 to ion milling from theside of the magnetic layer 115, depth profile analysis of the magneticlayer 115 is carried out by AES, and the average compositions (averageatomic ratios) of Co, Pt, Cr, S1, and 0 in the film thickness directionare obtained.

The average thickness t_(m) [nm] of the magnetic layer 115 is preferably9 nm≤t_(m)≤90 nm, more preferably 9 nm≤t_(m)≤20 nm, and even morepreferably 9 nm≤t_(m)≤15 nm. If the average thickness t_(m) of themagnetic layer 115 is within the above-described value range, theelectromagnetic conversion characteristic is improved.

(Protective Layer)

The protective layer 116 includes, for example, a carbon material orsilicon dioxide (SiO₂), and preferably includes a carbon material fromthe viewpoint of the film intensity of the protective layer 116.Examples of the carbon material include graphite, diamond-like carbon(DLC), or diamond.

(Lubricating Layer)

The lubricating layer 117 includes at least one lubricant. Thelubricating layer 117 may further include, as necessary, variousadditives such as a rust-preventive agent. The lubricant has at leasttwo carboxyl groups and one ester bond, and includes at least onecarboxylic acid compound represented by the following general formula(1). The lubricant may further include another lubricant other than thecarboxylic acid compound represented by the following general formula(1).

General Formula (1):

(In the formula, Rf is an unsubstituted or substituted saturated orunsaturated fluorine-containing hydrocarbon group or a hydrocarbongroup, Es is an ester bond, and R may be omitted, or is an unsubstitutedor substituted saturated or unsaturated hydrocarbon group.)

The carboxylic acid compound is preferably represented by the followinggeneral formula (2) or (3).

General Formula (2):

(In the formula, Rf is an unsubstituted or substituted saturated orunsaturated fluorine-containing hydrocarbon group or a hydrocarbongroup.)

General Formula (3):

(In the formula, Rf is an unsubstituted or substituted saturated orunsaturated fluorine-containing hydrocarbon group or a hydrocarbongroup.)

The lubricant preferably includes one or both of the carboxylic acidcompounds represented by the general formulae (2) and (3).

If a lubricant containing the carboxylic acid compound represented bythe general formula (1) is applied to, for example, the magnetic layer115 or the protective layer 116, lubrication effect is expressed bycohesive force between the fluorine-containing hydrocarbon groups orhydrocarbon groups Rf which are hydrophobic groups. In a case where theRf group is a fluorine-containing hydrocarbon group, the total carbonnumber is preferably 6 to 50, and the total carbon number of afluorohydrocarbon group is preferably 4 to 20. The Rf group may be, forexample, a saturated or unsaturated linear, branched, or cyclichydrocarbon group, and may be preferably a saturated linear hydrocarbongroup.

For example, in a case where the Rf group is a hydrocarbon group, thegroup is preferably the group represented by the following generalformula (4).

General Formula (4):

(Note that in the general formula (4), 1 is an integer selected from therange of 8 to 30 and more preferably 12 to 20.)

Additionally, in a case where the Rf group is a fluorine-containinghydrocarbon group, the group is preferably the group represented by thefollowing general formula (5).

General Formula (5):

(Note that in the general formula (5), m and n are integersindependently selected from the following ranges: m=2 to 20, n=3 to 18,and more preferably m=4 to 13, n=3 to 10, respectively.)

The fluorinated hydrocarbon group may be concentrated in one point in amolecule as depicted above, or dispersed as depicted in the followinggeneral formula (6), and may be, for example, —CF₃, —CF₂—, —CHF₂—, orCHF—.

General Formula (6):

(Note that in the general formulae (5) and (6), n1+n2=n and m1+m2=m.)

In the general formulae (4), (5), and (6), the reason that the carbonnumber is limited as described above is as follows. If the number of thecarbon atoms composing an alkyl group or a fluorine-containing alkylgroup (l or the sum of m and n) is not less than the above-describedlower limit, the length is appropriate, cohesive force betweenhydrophobic groups is effectively exerted, good lubrication effect isdeveloped, and friction and abrasion durability is improved.Additionally, if the carbon number is not more than the upper limit, thelubricant including the above-described carboxylic acid compoundmaintains good solubility in a solvent.

In particular, if the Rf groups in the general formulae (1), (2), and(3) include a fluorine atom, they are effective for reduction of thecoefficient of friction and improvement of traveling properties.However, it is preferred that a hydrocarbon group be provided between afluorine-containing hydrocarbon group and an ester bond to separate thefluorine-containing hydrocarbon group and the ester bond, therebyensuring stability of the ester bond to prevent hydrolysis.Additionally, the Rf group may have a fluoro alkyl ether group or aperfluoro polyether group. The R group in the general formula (1) may beomitted, but if the group is present, it is preferably a hydrocarbonchain with a relatively small carbon number.

Additionally, the Rf group or R group includes, as constitutionalelement, one or a plurality of elements selected from nitrogen, oxygen,sulfur, phosphorus, and halogen, and beside the above-describedfunctional group, may further have, for example, a hydroxyl group, acarboxyl group, a carbonyl group, an amino group, and an ester bond.

Specifically, the carboxylic acid compound represented by the generalformula (1) is preferably at least one of the compounds listed below.More specifically, the lubricant preferably includes at least one of thefollowing compounds.

CF₃(CF₂)₇(CH₂)₁₀COOCH(COOH)CH₂COOH

CF₃(CF₂)₃(CH₂)₁₀COOCH(COOH)CH₂COOH

C₁₇H₃₅COOCH(COOH)CH₂COOH

CF₃(CF₂)₇(CH₂)₂OCOCH₂CH(C₁₈H₃₇)COOCH(COOH)CH₂COOH

CF₃(CF₂)₇COOCH(COOH)CH₂COOH

CHF₂(CF₂)₇COOCH(COOH)CH₂COOH

CF₃(CF₂)₇(CH₂)₂OCOCH₂CH(COOH)CH₂COOH

CF₃(CF₂)₇(CH₂)₆OCOCH₂CH(COOH)CH₂COOH

CF₃(CF₂)₇(CH₂)₁₁OCOCH₂CH(COOH)CH₂COOH

CF₃(CF₂)₃(CH₂)₆OCOCH₂CH(COOH)CH₂COOH

C₁₈H₃₇OCOCH₂CH(COOH)CH₂COOH

CF₃(CF₂)₇(CH₂)₄COOCH(COOH)CH₂COOH

CF₃(CF₂)₃(CH₂)₄COOCH(COOH)CH₂COOH

CF₃(CF₂)₃(CH₂)₇COOCH(COOH)CH₂COOH

CF₃(CF₂)₉(CH₂)₁₀COOCH(COOH)CH₂COOH

CF₃(CF₂)₇(CH₂)₁₂COOCH(COOH)CH₂COOH

CF₃(CF₂)₅(CH₂)₁₀COOCH(COOH)CH₂COOH

CF₃(CF₂)₇CH(C₉H₁₉)CH₂CH═CH(CH₂)₇COOCH(COOH)CH₂COOH

CF₃(CF₂)₇CH(C₆H₁₃)(CH₂)₇COOCH(COOH)CH₂COOH

CH₃(CH₂)₃(CH₂CH₂CH(CH₂CH₂(CF₂)₉CF₃))₂(CH₂)₇COOCH(COOH)CH₂COOH

The carboxylic acid compound represented by the general formula (1) issoluble in a non-fluorine solvent having a low impact on theenvironment, and allows operations such as application, immersion, andspraying using a general-purpose solvent such as a hydrocarbon solvent,a ketone solvent, an alcohol solvent, and an ester solvent. Specificexamples of the general-purpose solvent include hexane, heptane, octane,decane, dodecane, benzene, toluene, xylene, cyclohexane, methyl ethylketone, methyl isobutyl ketone, methanol, ethanol, isopropanol, diethylether, tetrahydrofuran, dioxane, and cyclohexanone.

In a case where the protective layer 116 includes a carbon material, ifthe carboxylic acid compound as a lubricant is applied to the protectivelayer 116, two carboxyl groups and at least one ester linking group,which are polar groups of the lubricant molecule, are adsorbed to theprotective layer 116, and a lubricating layer 117 having particularlygood durability is formed by cohesive force between the hydrophobicgroups.

Note that the lubricant may be held as the lubricating layer 117 on thesurface of the magnetic recording medium 110 as described above, orincluded and held in, for example, the magnetic layer 115 and theprotective layer 116 composing the magnetic recording medium 110.

(Back Layer)

For the back layer 118, description about the back layer 14 in the firstembodiment holds true.

(3) Physical Properties and Structure

All descriptions about the physical properties and configuration givenin 2.(3) hold true for the second embodiment. For example, the averagethickness t_(T), the dimensional variation Δw, the thermal expansioncoefficient α, the humidity expansion coefficient β, the Poisson's ratioρ, the elastic limit value σ_(MD) in the longitudinal direction, thecoefficient of friction μ between the magnetic surface and the backsurface, the surface roughness R_(ab) of the back layer 118, the rate ofshrinkage in the longitudinal direction, and the 1% elongation load inthe longitudinal direction of the magnetic recording medium 110 may besimilar to those in the first embodiment. Therefore, descriptions aboutthe physical properties and configuration of the magnetic recordingmedium according to the second embodiment are omitted.

(4) Configuration of Sputtering Apparatus

With reference to FIG. 9, an example of the configuration of asputtering apparatus 120 used for producing the magnetic recordingmedium 110 according to the second embodiment is described below. Thesputtering apparatus 120 is a sputtering apparatus of continuous windingtype used for forming the SUL 112, the first seed layer 113A, the secondseed layer 113B, the first primary layer 114A, the second primary layer114B, and the magnetic layer 115, and includes, as depicted in FIG. 9, adeposition chamber 121, a drum 122 as a metal can (rotating body),cathodes 123 a to 123 f, a supply reel 124, a winding reel 125, and aplurality of guide rolls 127 a to 127 c and 128 a to 128 c. Thesputtering apparatus 120 is, for example, an apparatus of direct current(DC) magnetron sputtering system, but the sputtering system will not belimited to this system.

The deposition chamber 121 is connected to a vacuum pump (not depicted)through an air exit 126, and the vacuum pump sets the atmosphere in thedeposition chamber 121 at the predetermined degree of vacuum. In thedeposition chamber 121, the drum 122 having a rotatable configuration,the supply reel 124, and the winding reel 125 are arranged. In thedeposition chamber 121, the plurality of guide rolls 127 a to 127 c forguiding transfer of the base layer 111 between the supply reel 124 andthe drum 122 is provided, and the plurality of guide rolls 128 a to 128c for guiding transfer of the base layer 111 between the drum 122 andthe winding reel 125 is provided. During sputtering, the base layer 111wound off from the supply reel 124 is wound up by the winding reel 125through the guide rolls 127 a to 127 c, the drum 122, and the guiderolls 128 a to 128 c. The drum 122 has a cylindrical shape, and the longbase layer 111 is transferred along the circumference columnar surfaceof the drum 122. The drum 122 includes a cooling mechanism (notdepicted), and is cooled to, for example, about −20° C. duringsputtering. In the deposition chamber 121, the plurality of cathodes 123a to 123 f is arranged opposed to circumference surface of the drum 122.Each of these cathodes 123 a to 123 f has a target. Specifically, thecathodes 123 a, 123 b, 123 c, 123 d, 123 e, and 123 f have targets forforming the SUL 112, the first seed layer 113A, the second seed layer113B, the first primary layer 114A, the second primary layer 114B, andthe magnetic layer 115, respectively. These cathodes 123 a to 123 fsimultaneously form a plurality of kinds of films, more specifically,the SUL 112, the first seed layer 113A, the second seed layer 113B, thefirst primary layer 114A, the second primary layer 114B, and themagnetic layer 115.

The sputtering apparatus 120 having the above-described configurationcontinuously forms the SUL 112, the first seed layer 113A, the secondseed layer 113B, the first primary layer 114A, the second primary layer114B, and the magnetic layer 115 by the Roll to Roll method.

(5) Method for Producing Magnetic Recording Medium

The magnetic recording medium 110 according to the second embodiment maybe produced, for example, as follows.

Firstly, using the sputtering apparatus 120 depicted in FIG. 9, the SUL112, the first seed layer 113A, the second seed layer 113B, the firstprimary layer 114A, the second primary layer 114B, and the magneticlayer 115 are formed in this order on the surface of the base layer 111.Specifically, these films are formed as follows. Firstly, the depositionchamber 121 is vacuumed to a predetermined pressure. Thereafter, thetargets set on the cathodes 123 a to 123 f are sputtered whileintroducing a process gas such as Ar gas into the deposition chamber121.

As a result of this, the SUL 112, the first seed layer 113A, the secondseed layer 113B, the first primary layer 114A, the second primary layer114B, and the magnetic layer 115 are formed in this order on the surfaceof the traveling base layer 111.

The atmosphere in the deposition chamber 121 during sputtering is setat, for example, about 1×10⁻⁵ Pa to 5×10⁻⁵ Pa. The film thicknesses andcharacteristics of the SUL 112, the first seed layer 113A, the secondseed layer 113B, the first primary layer 114A, the second primary layer114B, and the magnetic layer 115 can be controlled by adjusting the tapeline velocity of winding the base layer 111, the pressure of the processgas such as Ar gas introduced during sputtering (sputtering gaspressure), the input power, and the like.

Subsequently, the protective layer 116 is formed on the magnetic layer115. The method for forming the protective layer 116 may be, forexample, a chemical vapor deposition (CVD) method or a physical vapordeposition (PVD) method.

Subsequently, a binder, inorganic particles, a lubricant, and others aremixed with and dispersed in a solvent, thereby preparing a back layerforming paint. Subsequently, the back layer forming paint is applied tothe back surface of the base layer 111 and dried, thus forming the backlayer 118 on the back surface of the base layer 111.

Subsequently, for example, a lubricant is applied to the protectivelayer 116, thus forming the lubricating layer 117. Application of thelubricant may use various application methods such as gravure coatingand dip coating. Subsequently, as necessary, the magnetic recordingmedium 110 is cut to a predetermined width. In this manner, the magneticrecording medium 110 depicted in FIG. 8 is obtained.

(6) Effect

In the magnetic recording medium 110 according to the second embodiment,in a manner similar to the first embodiment, change in the width of themagnetic recording medium 110 can be suppressed by adjusting the tensionof the magnetic recording medium 110 in the longitudinal direction usinga recording and reproducing apparatus. For example, even if temperatureand humidity change, which can change the width of the magneticrecording medium 110, occurs, the width of the magnetic recording medium110 is kept constant or generally constant. The suppression of widthchange by the tension adjustment is possible even after long-termstorage. Furthermore, the magnetic recording medium 110 is as thin ast_(T)≤5.5 μm, but has marked handleability.

(7) Modification

The magnetic recording medium 110 may further include a primary layerbetween the base layer 111 and the SUL 112. The SUL 112 has an amorphousstate, and thus does not have a role to promote epitaxial growth of thelayer formed on the SUL 112, but may be required not to disturb thecrystal orientation of the first and second primary layers 114A and 114Bformed on the SUL 112. In order to achieve this, the soft magneticmaterial preferably has a fine structure which will not form a column.However, in a case where the influence of degassing such as moisturefrom the base layer 111 is considerable, the soft magnetic material maybe coarsened to disturb the crystal orientation of the first and secondprimary layers 114A and 114B formed on the SUL 112. In order to suppressthe influence of degassing such as moisture from the base layer 111, asdescribed above, it is preferred that a primary layer, which includes analloy containing Ti and Cr and has amorphous state, is provided betweenthe base layer 111 and the SUL 112. Specific configuration of theprimary layer may adopt the configuration similar to that of the firstseed layer 113A of the second embodiment.

The magnetic recording medium 110 may not include at least one of thesecond seed layer 113B or the second primary layer 114B. However, fromthe viewpoint of improvement of SNR, it is more preferred that both ofthe second seed layer 113B and the second primary layer 114B beincluded.

The magnetic recording medium 110 may include APC-SUL (antiparallelcoupled SUL) in place of single layer SUL.

4. THIRD EMBODIMENT (EXAMPLE OF MAGNETIC RECORDING MEDIUM OF VACUUM THINFILM TYPE)

(Configuration of Magnetic Recording Medium)

A magnetic recording medium 130 according to the third embodimentincludes, as depicted in FIG. 10, a base layer 111, a SUL 112, a seedlayer 131, a first primary layer 132A, a second primary layer 132B, anda magnetic layer 115. Note that, in the third embodiment, points similarto the second embodiment are indicated with the same reference numerals,and descriptions thereof are omitted.

The SUL 112, the seed layer 131, and the first and second primary layers132A and 132B are provided between the one main surface of the baselayer 111 and the magnetic layer 115, and the SUL 112, the seed layer131, the first primary layer 132A, and the second primary layer 132B arelaminated in this order in a direction from the base layer 111 towardthe magnetic layer 115.

(Seed Layer)

The seed layer 131 includes Cr, Ni, and Fe, has a face-centered cubiclattice (fcc) structure, and the (111) face of the face-centered cubicstructure is preferentially oriented so as to be parallel to the surfaceof the base layer 111. The term preferential orientation means that thediffraction peak intensity from the (111) face of the face-centeredcubic lattice structure is higher than the diffraction peak from othercrystal face in the θ-2θ scanning by X-ray diffractometry, or only thediffraction peak intensity from the (111) face of the in face-centeredcubic lattice structure is observed in the θ-2θ scanning by X-raydiffractometry.

The intensity ratio of X-ray diffraction of the seed layer 131 ispreferably 60 cps/nm or more, more preferably 70 cps/nm or more, andeven more preferably 80 cps/nm or more, from the viewpoint ofimprovement of SNR. Here, the intensity ratio of X-ray diffraction ofthe seed layer 131 is a value (I/D (cps/nm)) determined by dividing theintensity I (cps) of X-ray diffraction of the seed layer 131 by theaverage thickness D (nm) of the seed layer 131.

Cr, Ni, and Fe included in the seed layer 131 preferably have theaverage composition represented by the following formula (2).Cr_(X)(Ni_(Y)Fe_(100-Y))_(100-X)  (2)

(Note that in the formula (2), X and Y are within the ranges of 10≤X≤45and 60≤Y≤90.) If X is within the above-described range, the (111)orientation of the face-centered cubic lattice structure of Cr, Ni, andFe improves, whereby better SNR is obtained. In a similar way, if Y iswithin the above-described range, the (111) orientation of theface-centered cubic lattice structure of Cr, Ni, and Fe improves,whereby better SNR is obtained.

The average thickness of the seed layer 131 is preferably 5 nm or moreand 40 nm or less. If the average thickness of the seed layer 131 iswithin this range, the (111) orientation of the face-centered cubiclattice structure of Cr, Ni, and Fe improves, whereby better SNR isobtained.

Note that the average thickness of the seed layer 131 is determined in amanner similar to that of the magnetic layer 13 in the first embodiment.However, the magnification of the TEM image is adjusted as appropriateaccording to the thickness of the seed layer 131.

(First and Second Primary Layers)

The first primary layer 132A includes Co and O having a face-centeredcubic lattice structure, and has a column (columnar crystal) structure.The first primary layer 132A including Co and O achieves an effect(function) almost similar to that of the second primary layer 132Bincluding Ru. The concentration ratio of the average atom concentrationof O to the average atom concentration of Co ((average atomconcentration of O)/(average atom concentration of Co)) is 1 or more. Ifthe concentration ratio is 1 or more, the effect of providing the firstprimary layer 132A improves, whereby better SNR is obtained.

The column structure is preferably inclined from the viewpoint ofimprovement of SNR. The direction of the incline is preferably thelongitudinal direction of the long magnetic recording medium 130. Thereason for the preference for the longitudinal direction is as follows.The magnetic recording medium 130 according to the present embodiment isa magnetic recording medium for so-called linear recording, and therecording track is parallel to the longitudinal direction of themagnetic recording medium 130. Additionally, the magnetic recordingmedium 130 according to the present embodiment is also a so-calledvertical magnetic recording medium, and a crystal orientation axis ofthe magnetic layer 115 is preferably vertical direction from theviewpoint of recording characteristics, but the crystal orientation axisof the magnetic layer 115 may be declined by the influence of thedecline of the column structure of the first primary layer 132A. In themagnetic recording medium 130 for linear recording, in consideration ofthe relationship with the head magnetic field during recording, theconfiguration in which the crystal orientation axis of the magneticlayer 115 is inclined in the longitudinal direction of the magneticrecording medium 130 reduces the influence of the inclination of thecrystal orientation axis on recording characteristics in comparison withthe configuration in which the crystal orientation axis of the magneticlayer 115 is inclined in the width direction of the magnetic recordingmedium 130. In order to incline the crystal orientation axis of themagnetic layer 115 in the longitudinal direction of the magneticrecording medium 130, as described above, the inclination direction ofthe column structure of the first primary layer 132A is preferably thelongitudinal direction of the magnetic recording medium 130.

An inclination angle of the column structure is preferably more than 0°and 60° or less. If the inclination angle is more than 0° and 60° orless, the tip shape of the column included in the first primary layer132A is markedly changed to become a generally triangle shape, so thatthe effect of the granular structure increases, the noise reduces, andthe SNR tends to improve. On the other hand, if the inclination angle ismore than 60°, the tip shape of the column included in the first primarylayer 132A is little changed and hard to form a generally triangleshape, so that a noise reduction effect tends to decrease.

The average particle size of the column structure is 3 nm or more and 13nm or less. If the average particle size is less than 3 nm, the averageparticle size of the column structure included in the magnetic layer 115decreases, so that the capacity of the current magnetic material forholding recording may decrease. On the other hand, if the averageparticle size is 13 nm or less, noise is suppressed, and better SNR isobtained.

The average thickness of the first primary layer 132A is preferably 10nm or more and 150 nm or less. If the average thickness of the firstprimary layer 132A is 10 nm or more, the (111) orientation of theface-centered cubic lattice structure of the first primary layer 132Aimproves, and better SNR is obtained. On the other hand, if the averagethickness of the first primary layer 132A is 150 nm or less, theincrease of the particle size of column is suppressed.

Accordingly, noise is suppressed, better SNR is obtained. Note that theaverage thickness of the first primary layer 132A is determined in amanner similar to that of the magnetic layer 13 in the first embodiment.However, the magnification of the TEM image is adjusted as appropriateaccording to the thickness of the first primary layer 132A.

The second primary layer 132B preferably has a crystal structure similarto that of the magnetic layer 115. In a case where the magnetic layer115 includes a Co alloy, the second primary layer 132B preferablyincludes a material having a hexagonal close-packed (hcp) structuresimilar to that of the Co alloy, and the c axis of the structure ispreferably oriented in a vertical direction (more specifically filmthickness direction) relative to the film surface. This improvesorientation of the magnetic layer 115, and achieves relatively goodmatching of the lattice constants of the second primary layer 132B andthe magnetic layer 115. The material having a hexagonal close-packedstructure is preferably a Ru-containing material, specifically single Ruor a Ru alloy. Examples of the Ru alloy include Ru alloy oxides such asRu—SiO₂, Ru—TiO₂, or Ru—ZrO₂.

The average thickness of the second primary layer 132B may be smallerthan that of a primary layer (for example, a Ru-containing primarylayer) in a common magnetic recording medium, and may be, for example, 1nm or more and 5 nm or less. Since the seed layer 131 and the firstprimary layer 132A having the above-described configurations areprovided below the second primary layer 132B, so that good SNR isobtained even if the average thickness of the second primary layer 132Bis small as described above. Note that the average thickness of thesecond primary layer 132B is determined in a manner similar to that ofthe magnetic layer 13 in the first embodiment. However, themagnification of the TEM image is adjusted as appropriate according tothe thickness of the second primary layer 132B.

Effect

In the magnetic recording medium 130 according to the third embodiment,in a manner similar to the first embodiment, the width of the magneticrecording medium 10 can be kept constant or generally constant throughthe adjustment of the tension of the magnetic recording medium 10 in thelongitudinal direction.

The magnetic recording medium 130 according to the third embodimentincludes the seed layer 131 and the first primary layer 132A between thebase layer 111 and the second primary layer 132B. The seed layer 131includes Cr, Ni, and Fe, has a face-centered cubic lattice structure,and the (111) face of the face-centered cubic structure ispreferentially oriented so as to be parallel to the surface of the baselayer 111. The first primary layer 132A includes Co and O, the ratio ofthe average atom concentration of O to the average atom concentration ofCo is 1 or more, and has a column structure with an average particlesize of 3 nm or more and 13 nm or less. This allows the thickness of thesecond primary layer 132B to be reduced and minimizes the use of acostly material Ru, and allows the magnetic layer 115 having goodcrystal orientation and high antimagnetic force to be provided.

Ru included in the second primary layer 132B has the same hexagonalclose-packed lattice structure as Co, which is the main component of themagnetic layer 115. Therefore, Ru improves crystal orientation andpromotes granular properties of the magnetic layer 115.

Additionally, in order to further improve crystal orientation of Ruincluded in the second primary layer 132B, the first primary layer 132Aand the seed layer 131 are provided below the second primary layer 132B.In the magnetic recording medium 130 according to the third embodiment,the first primary layer 132A containing low-cost CoO having aface-centered cubic lattice structure achieves an effect (function)almost similar to the second primary layer 132B containing Ru. Thisallows reduction of the thickness of the second primary layer 132B.

Additionally, in order to increase crystal orientation of the firstprimary layer 132A, the seed layer 131 containing Cr, Ni, and Fe isprovided.

5. EXAMPLES

The present technology is specifically described by examples, but thepresent technology will not be limited to these examples.

In the following examples and comparative examples, the averagethickness t_(T) of the magnetic tape, the dimensional variation Δw ofthe magnetic tape in the width direction to the tension change of themagnetic tape in the longitudinal direction, the thermal expansioncoefficient α of the magnetic tape, the humidity expansion coefficient βof the magnetic tape, the Poisson's ratio ρ of the magnetic tape, theelastic limit value σ_(MD) of the magnetic tape in the longitudinaldirection, the average thickness t_(m) of the magnetic layer, thesquareness ratio S2, the average thickness t_(b) of the back layer, thesurface roughness R_(ab) of the back layer, the interlayer coefficientof friction μ between the magnetic surface and the back surface, therate of shrinkage in the longitudinal direction, and the 1% elongationload in the longitudinal direction are the values obtained by themeasurement method described in the first embodiment. As will bedescribed later, however, in Example 11, the velocity V in measurementof the elastic limit value a in the longitudinal direction was a valuedifferent from that obtained by the measurement method described in thefirst embodiment.

Example 1

(Preparation Process of Magnetic Layer Forming Paint)

A magnetic layer forming paint was prepared as follows. Firstly, a firstcomposition of the following recipe was kneaded with an extruder.Subsequently, the kneaded first composition and a second composition ofthe following recipe were placed in a stirring tank equipped with adisperser, and subjected to preliminary mixing. Subsequently, sand millmixing was further carried out, filter treatment was carried out, thuspreparing a magnetic layer forming paint.

(First Composition)

Powder of ε-iron oxide nanoparticles (ε-Fe₂O₃ crystal particles): 100parts by mass Vinyl chloride resin (cyclohexanone solution 30% by mass):10 parts by mass (degree of polymerization 300, Mn=10000, containingOSO₃K=0.07 mmol/g and secondary OH=0.3 mmol/g as polar groups)

Aluminum oxide powder: 5 parts by mass

(α-Al₂O₃, average particle size 0.2 μm)

Carbon black: 2 parts by mass

(trade name: SEAST TA, Tokai Carbon Co., Ltd.)

(Second Composition)

Vinyl chloride resin: 1.1 parts by mass

(resin solution: resin component 30% by mass, cyclohexanone 70% by mass)

n-butyl stearate: 2 parts by mass

Methyl ethyl ketone: 121.3 parts by mass

Toluene: 121.3 parts by mass

Cyclohexanone: 60.7 parts by mass

Finally, to the magnetic layer forming paint prepared as describedabove, as curing agents, 4 parts by mass of polyisocyanate (trade name:COLONATE L, Nippon Polyurethane Industry Co., Ltd.) and 2 parts by massof myristic acid were added.

(Preparation Process of Primary Layer Forming Paint)

A primary layer forming paint was prepared as follows. Firstly, a thirdcomposition of the following recipe was kneaded with an extruder.Subsequently, the kneaded third composition and a fourth composition ofthe following recipe were placed in a stirring tank equipped with adisperser, and subjected to preliminary mixing. Subsequently, the objectwas further subjected to sand mill mixing, filtered, thus preparing aprimary layer forming paint.

(Third Composition)

Needle-shaped iron oxide powder: 100 parts by mass

(α-Fe₂O₃, average major axis length 0.15 μm)

Vinyl chloride resin: 55.6 parts by mass

(Resin solution: resin component 30% by mass, cyclohexanone 70% by mass)

Carbon black: 10 parts by mass

(Average particle size 20 nm)

(Fourth Composition)

Polyurethane resin UR8200 (Toyobo Co., Ltd.): 18.5 parts by mass

n-butyl stearate: 2 parts by mass

Methyl ethyl ketone: 108.2 parts by mass

Toluene: 108.2 parts by mass

Cyclohexanone: 18.5 parts by mass

Finally, to the primary layer forming paint prepared as described above,as curing agents, 4 parts by mass of polyisocyanate (trade name:COLONATE L, Nippon Polyurethane Industry Co., Ltd.) and 2 parts by massof myristic acid were added.

(Preparation Process of Back Layer Forming Paint)

Aback layer forming paint was prepared as follows. The following rawmaterials were mixed with a stirring tank equipped with a disperser, andfiltered, thereby preparing a back layer forming paint.

Carbon black (Asahi Carbon Co., Ltd., trade name: #80): 100 parts bymass

Polyester polyurethane: 100 parts by mass

(Nippon Polyurethane Industry Co., Ltd., trade name: N-2304)

Methyl ethyl ketone: 500 parts by mass

Toluene: 400 parts by mass

Cyclohexanone: 100 parts by mass

(Deposition Process)

Using the paints prepared as described above, a primary layer having anaverage thickness of 1.0 m, and a magnetic layer having an averagethickness t_(m) of 90 nm were formed as follows on a long polyethylenenaphthalate film (hereinafter referred to as “PEN film”) as anon-magnetic support. Firstly, on the film, the primary layer formingpaint was applied and dried, thereby forming a primary layer on thefilm. Subsequently, on the primary layer, the magnetic layer formingpaint was applied and dried, thereby forming a magnetic layer on theprimary layer.

Note that, in drying of the magnetic layer forming paint, the magneticfield of the magnetic powder was oriented in the thickness direction ofthe film using a solenoid coil. Additionally, the time of application ofa magnetic field to the magnetic layer forming paint was adjusted so asto set the squareness ratio S2 of the magnetic tape in the thicknessdirection (vertical direction) at 65%.

Subsequently, to the film having the primary layer and the magneticlayer, a back layer having an average thickness t_(b) of 0.6 μm wasapplied and dried. Then, the film having the primary layer, the magneticlayer, and the back layer was subjected to curing treatment.Subsequently, the film was subjected to calendar processing, therebysmoothening the surface of the magnetic layer. At this time, theconditions (temperature) of calendar processing were adjusted so as toachieve an interlayer coefficient of friction μ of about 0.5 between themagnetic surface and the back surface, and then the film was subjectedto re-curing treatment, thus obtaining a magnetic tape having an averagethickness t_(T) of 5.5 μm.

(Cutting Process)

The magnetic tape obtained as described above was cut to a ½-inch (12.65mm) width, and wound on a core, thus obtaining a pancake.

The magnetic tape obtained as described above had the characteristicsgiven in Table 1. For example, the dimensional variation ΔW of themagnetic tape was 705 ppm/N, and the rate of shrinkage in thelongitudinal direction was 0.05%.

Example 2

A magnetic tape was obtained in the same manner as in Example 1, exceptthat the thickness of the PEN film was decreased than that in Example 1so as to achieve a dimensional variation Δw of 750 ppm/N. The averagethickness t_(T) of the magnetic tape was 5 μm.

Example 3

A magnetic tape was obtained in the same manner as in Example 1, exceptthat the thickness of the PEN film was decreased and the averagethicknesses of the back layer and the primary layer were decreased fromthose in Example 1 so as to achieve a dimensional variation Δw of 800ppm/N. The average thickness t_(T) of the magnetic tape was 4.5 μm.

Example 4

A magnetic tape was obtained in the same manner as in Example 1, exceptthat the thickness of the PEN film was decreased and the averagethicknesses of the back layer and the primary layer were decreased fromthose in Example 1, and the curing treatment conditions of the filmhaving the primary layer, the magnetic layer, and the back layer wereadjusted so as to achieve a dimensional variation Δw of 800 ppm/N.

Example 5

A magnetic tape was obtained in the same manner as in Example 4, exceptthat the composition of the primary layer forming paint was changed soas to achieve a thermal expansion coefficient α of 8.0 ppm/° C.

Example 6

A magnetic tape was obtained in the same manner as in Example 4, exceptthat a thin barrier layer was formed on the both surfaces of the PENfilm so as to achieve a humidity expansion coefficient β of 3.0 ppm/%RH.

Example 7

A magnetic tape was obtained in the same manner as in Example 4, exceptthat the composition of the back layer forming paint was changed so asto achieve a Poisson's ratio ρ of 0.31.

Example 8

A magnetic tape was obtained in the same manner as in Example 4, exceptthat the composition of the back layer forming paint was changed so asto achieve a Poisson's ratio ρ of 0.35.

Example 9

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the curing conditions for the film having a primary layer, amagnetic layer, and a back layer were changed so as to achieve anelastic limit value σ_(MD) of 0.8 N in the longitudinal direction.

Example 10

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the curing conditions and the re-curing conditions for the filmhaving the primary layer, the magnetic layer, and the back layer werechanged so as to achieve an elastic limit value σ_(MD) of 3.5 N in thelongitudinal direction.

Example 11

A magnetic tape was obtained in a similar manner as in Example 9. Then,the elastic limit value σ_(MD) of the magnetic tape thus obtained wasmeasured with the velocity V in measuring the elastic limit value σ_(MD)in the longitudinal direction changed to 5 mm/min. As a result of this,the elastic limit value σ_(MD) in the longitudinal direction was 0.8,which was not different from the elastic limit value σ_(MD) in thelongitudinal direction when the velocity V was 0.5 mm/min (Example 9).

Example 12

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the coating thickness of the magnetic layer forming paint waschanged so as to achieve an average thickness t_(m) of the magneticlayer of 40 nm.

Example 13

(SUL Deposition Process)

Firstly, a CoZrNb layer (SUL) with an average thickness of 10 nm wasdeposited on the surface of a long polymer film as a non-magneticsupport under the following deposition conditions. Note that a PEN filmwas used as the polymer film.

Film formation system: DC magnetron sputtering system

Target: CoZrNb target

Gas type: Ar

Gas pressure: 0.1 Pa

(Deposition Process of First Seed Layer)

Subsequently, under the following deposition conditions, a TiCr layerhaving an average

thickness of 5 nm (first seed layer) was deposited on the CoZrNb layer.

Sputtering system: DC magnetron sputtering system

Target: TiCr target

Ultimate vacuum: 5×10⁻⁵ Pa

Gas type: Ar

Gas pressure: 0.5 Pa

(Deposition Process of Second Seed Layer)

Subsequently, under the following deposition conditions, a NiW layerhaving an average

thickness of 10 nm (second seed layer) was deposited on the TiCr layer.

Sputtering system: DC magnetron sputtering system

Target: NiW target

Ultimate vacuum: 5×10⁻⁵ Pa

Gas type: Ar

Gas pressure: 0.5 Pa

(Deposition Process for First Primary Layer)

Subsequently, under the following deposition conditions, a Ru layerhaving an average thickness

of 10 nm (first primary layer) was deposited on the NiW layer.

Sputtering system: DC magnetron sputtering system

Target: Ru target

Gas type: Ar

Gas pressure: 0.5 Pa

(Deposition Process for Second Primary Layer)

Subsequently, under the following deposition conditions, a Ru layerhaving an average thickness of 20 nm (second primary layer) wasdeposited on the Ru layer.

Sputtering system: DC magnetron sputtering system

Target: Ru target

Gas type: Ar

Gas pressure: 1.5 Pa

(Deposition Process for Magnetic Layer)

Subsequently, under the following deposition conditions, a(CoCrPt)—(SiO₂) layer having an

average thickness 9 nm (magnetic layer) was deposited on the Ru layer.

Deposition system: DC magnetron sputtering system

Target: (CoCrPt)—(SiO₂) target

Gas type: Ar

Gas pressure: 1.5 Pa

(Deposition Process for Protective Layer)

Subsequently, under the following deposition conditions, a carbon layer(protective layer) having

an average thickness of 5 nm was deposited on the magnetic layer.

Deposition system: DC magnetron sputtering system

Target: carbon target

Gas type: Ar

Gas pressure: 1.0 Pa

(Deposition Process for Lubricating Layer)

Subsequently, a lubricant was applied to the protective layer, thusforming a lubricating layer.

(Deposition Process for Back Layer)

Subsequently, on a surface opposite to the magnetic layer, a back layerforming paint was applied and dried, thereby forming a back layer havingan average thickness t_(b) of 0.3 μm. As a result of this, a magnetictape having an average thickness t_(T) of 4.0 μm was obtained.

(Cutting Process)

The magnetic tape obtained as described above was cut to a ½-inch (12.65mm) width. The magnetic tape obtained as described above had thecharacteristics given in Table 1. For example, the dimensional variationΔW of the magnetic tape was 800 ppm/N, and the rate of shrinkage in thelongitudinal direction was 0.07%.

Example 14

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the thickness of the back layer was changed to 0.2 μm. The averagethickness of the magnetic tape was 4.4 μm.

Example 15

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the composition of the back layer forming paint was changed so asto achieve a surface roughness R_(ab) of the back layer of 3.4 nm.

Example 16

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the conditions (temperature) of calendaring were adjusted so as toachieve a coefficient of friction μ of 0.20.

Example 17

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the composition of the back layer forming paint was changed so asto achieve a surface roughness R_(ab) of the back layer of 3.2 nm andthe conditions (temperature) of calendaring were adjusted so as toachieve a coefficient of friction μ of 0.78.

Example 18

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the coating thickness of the magnetic layer forming paint waschanged so as to achieve an average thickness t_(m) of the magneticlayer of 110 nm.

Example 19

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the composition of the back layer forming paint was changed so asto achieve a surface roughness R_(ab) of the back layer of 7.2 nm.

Example 20

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the conditions (temperature) of calendaring were adjusted so as toachieve a coefficient of friction μ of 0.18.

Example 21

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the conditions (temperature) of calendaring were adjusted so as toachieve a coefficient of friction μ of 0.82.

Example 22

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the time of application of a magnetic field to the magnetic layerforming paint was adjusted so as to set the squareness ratio S2 of themagnetic tape in the thickness direction (vertical direction) at 73%.

Example 23

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the time of application of a magnetic field to the magnetic layerforming paint was adjusted so as to set the squareness ratio S2 of themagnetic tape in the thickness direction (vertical direction) at 80%.

Example 24

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the curing conditions and re-curing conditions for the film havingthe primary layer, the magnetic layer, and the back layer were adjustedso as to achieve an elastic limit value σ_(MD) of 5 N in thelongitudinal direction.

Example 25

A magnetic tape was obtained in the same manner as in Example 7, exceptthat barium ferrite (BaFe₁₂O₁₉) nanoparticles were used in place ofε-iron oxide nanoparticles.

Example 26

A magnetic tape was obtained in the same manner as in Example 25, exceptthat tensilization of the PEN film was changed so as to achieve adimensional variation Δw of 670 [ppm/N].

Example 27

A magnetic tape was obtained in the same manner as in Example 1, exceptthat tensilization of the PEN film was changed so as to achieve adimensional variation Δw of 650 [ppm/N].

Comparative Example 1

A magnetic tape was obtained in the same manner as in Example 1, exceptthat the tensilization of the PEN film was changed and the windingtension was increased in the application process so as to achieve adimensional variation Δw of 650 [ppm/N]. The rate of shrinkage of themagnetic tape in the longitudinal direction was 0.09%.

Comparative Example 2

A magnetic tape was obtained in the same manner as in Example 7, exceptthat the winding tension in the application process was increased. Therate of shrinkage of the magnetic tape in the longitudinal direction was0.11%.

Comparative Example 3

A magnetic tape was obtained in the same manner as in Example 7, exceptthat barium ferrite (BaFe₁₂O₁₉) nanoparticles were used in place ofε-iron oxide nanoparticles, and the tensilization of the PEN film waschanged so as to achieve a dimensional variation Δw of 630 [ppm/N]. Theaverage thickness t_(T) of the magnetic tape was 5.7 μm.

(Judgement of Tape Width Variation)

Firstly, a cartridge sample incorporating a magnetic tape having a widthof ½ inches was provided. In the cartridge sample, the magnetic tape iswound around the reel included in the cartridge case. Note that, on themagnetic tape, two or more lines of magnetic pattern in an inverted Vshape were preliminarily recorded in parallel to the longitudinaldirection at known intervals (hereinafter referred to as “known intervalof magnetic pattern lines in preliminary recording). Subsequently, thecartridge sample was reciprocally traveled with the recording andreproducing apparatus. Then, during the reciprocal traveling, two ormore of the magnetic pattern lines in an inverted V shape weresimultaneously reproduced, and the interval of the magnetic pattern lineduring traveling was continuously measured from the shape of thereproduction waveform of each line. Additionally, during traveling, onthe basis of the interval information of the magnetic pattern line thusmeasured, the rotational driving of the spindle driving apparatus andthe reel driving apparatus is controlled, and the tension of themagnetic tape in the longitudinal direction was automatically adjustedin such a manner that the interval of the magnetic pattern line was thedesired width, or generally the desired width. All the measurements ofone reciprocation of the interval of the magnetic pattern lines weresimply averaged and set as “the interval between the measured magneticpattern lines”, and the difference from “the distance of known magneticpattern lines which have been recorded” was set as “change of tapewidth”.

Additionally, the reciprocal traveling by the recording and reproducingapparatus was carried out in a thermohygrostat bath. The speed of thereciprocal traveling was 5 m/sec. The temperature and humidity duringreciprocal traveling were gradually and repeatedly changed independentfrom the above-described reciprocal traveling, according to a presetenvironmental change program (10° C., 10%→29° C., 80%→10° C., 10% isrepeated twice. 10° C., 10% is changed to 29° C., 80% over a period oftwo hours, and 29° C., 80% is changed to 10° C., 10% over a period oftwo hours) in the temperature range of 10° C. to 45° C. and the relativehumidity range of 10% to 80%.

This evaluation was repeated until the “preset environmental variationprogram” was completed. After completion of the evaluation, the average(simple average) was calculated using all the absolute values of each“change of tape width” obtained in each reciprocation, and the value wasrecorded as “variation of effective tape width” of the tape. Thejudgement according to alienation of the “variation of effective tapewidth” from the ideal (preferably as small as possible) was carried outon each tape, and eight grades were given. Note that the grade “8” isthe most desirable grade, and the grade “1” is the most undesirablegrade. In the magnetic tape evaluated as any of the eight grades, any ofthe following states is observed during tape traveling.

8: No abnormality occurs.

7: A mild increase of the error rate is observed during traveling.

6: A heavy increase of the error rate is observed during traveling.

5: Servo signal is not read during traveling, and mild reloading (one totwo times) is necessary.

4: Servo signal is not read during traveling, and moderate reloading(within ten times) is necessary.

3: Servo signal is not read during traveling, and heavy reloading (morethan ten times) is necessary.

2: Servo is not read, and traveling occasionally stops because of systemerror.

1: Servo is not read, and traveling instantly stops because of systemerror.

Furthermore, the magnetic tape loaded in a cartridge was stored for oneweek in an environment at 50° C. and 50% Rh, and then the same judgementwas carried out.

(Evaluation of Electromagnetic Conversion Characteristic)

Firstly, using a loop tester (Microphysics), a reproducing signal of themagnetic tape was acquired. The conditions for acquiring the reproducingsignal are given below.

Head: GMR

Head speed: 2 m/s

Signal: single recording frequency (10 MHz)

Recording current: optimum recording current

Subsequently, the reproducing signal was taken with a spectrum analyzerat a span of 0 to 20 MHz (resolution band width=100 kHz, VBW=30 kHz).Subsequently, the peak of the spectrum thus taken was recorded as thesignal amount S, and the floor noise excluding the peak was summed up toobtain the noise amount N, and the ratio of the signal amount S to thenoise amount N (S/N) was obtained as the signal-to-noise ratio (SNR).Subsequently, the SNR thus obtained was converted to a relative value(dB) based on the SNR of Comparative Example 1 as the reference medium.Subsequently, using the SNR (dB) obtained as described above, thequality of the electromagnetic conversion characteristic was judged asfollows.

Better: the SNR of the magnetic tape is 1 dB or more higher than the SNR(=0 (dB)) of the evaluation reference sample (Comparative Example 1).

Good: the SNR of the magnetic tape is equivalent to the SNR (=0 (dB)) ofthe evaluation reference sample (Comparative Example 1), or more thanthe SNR (=0 (dB)).

Bad: the SNR of the magnetic tape is less than the SNR (=0 (dB)) of theevaluation reference sample (Comparative Example 1).

(Evaluation of Winding Deviation)

Firstly, the cartridge sample after “judgement of tape width variation”was provided. Subsequently, the reel wound with the tape was taken outfrom the cartridge, and the end surface of the wound tape was visuallyobserved. Note that the reel has flanges, and at least one of theflanges is transparent or translucent, so that the internal state of thewound tape can be observed through the flange.

In the observation, in a case where the end surface of the tape is notflat, and a level difference or projecting of the tape is found, thetape is judged to have a winding deviation. Additionally, the degree of“winding deviation” was graded lower with the increase of the number ofsuch level differences and projecting of the tape. The above-describedjudgement was carried out for each sample. The winding deviationcondition of each sample was compared with the winding deviationcondition of Comparative Example 1 as a reference medium, and thequality was judged as follows.

Good: Winding deviation condition of the sample is equivalent to orlighter than the winding deviation condition of the reference sample(Comparative Example 1).

Bad: Winding deviation condition of the sample is heavier than thewinding deviation condition of the reference sample (Comparative Example1).

Table 1 lists the configurations and evaluation results of the magnetictapes of Examples 1 to 22 and Comparative Examples 1 to 5.

TABLE 1 Base layer Magnetic thickness t_(T) ΔW α β body (μm) (μm)(ppm/N) (ppm/° C.) (ppm/% RH) ρ Example 1 ε iron oxide 3.8 5.5 705 5.95.2 0.29 Example 2 ε iron oxide 3.3 5 750 5.9 5.2 0.29 Example 3 ε ironoxide 3.2 4.5 800 5.9 5.2 0.29 Example 4 ε iron oxide 3.2 4.5 800 6.05.0 0.29 Example 5 ε iron oxide 3.2 4.5 800 8.0 5.0 0.29 Example 6 εiron oxide 3.2 4.6 800 6.0 3.0 0.29 Example 7 ε iron oxide 3.2 4.5 8006.0 5.0 0.31 Example 8 ε iron oxide 3.2 4.5 800 6.0 5.0 0.35 Example 9 εiron oxide 3.2 4.5 800 6.0 5.0 0.31 Example 10 ε iron oxide 3.2 4.5 8006.0 5.0 0.31 Example 11 ε iron oxide 3.2 4.5 800 6.0 5.0 0.31 Example 12ε iron oxide 3.2 4.4 800 6.0 5.0 0.31 Example 13 CoPtCrSi 3.6 4 800 6.05.0 0.31 alloy Example 14 ε iron oxide 3.2 4.4 800 6.0 5.0 0.31 Example15 ε iron oxide 3.2 4.5 800 6.0 5.0 0.31 Example 16 ε iron oxide 3.2 4.5800 6.0 5.0 0.31 Example 17 ε iron oxide 3.2 4.5 800 6.0 5.0 0.31Example 18 ε iron oxide 3.2 4.5 800 6.0 5.0 0.31 Example 19 ε iron oxide3.2 4.5 800 6.0 5.0 0.31 Example 20 ε iron oxide 3.2 4.5 800 6.0 5.00.31 Example 21 ε iron oxide 3.2 4.5 800 6.0 5.0 0.31 Example 22 ε ironoxide 3.2 4.5 800 6.0 5.0 0.31 Example 23 ε iron oxide 3.2 4.5 800 6.05.0 0.31 Example 24 ε iron oxide 3.2 4.5 800 6.0 5.0 0.31 Example 25BaFe 3.2 4.5 800 6.0 5.0 0.31 Example 26 BaFe 3.2 4.5 670 6.0 5.0 0.31Example 27 ε iron oxide 3.8 5.5 650 5.9 5.2 0.29 Comparative 1 ε ironoxide 3.8 5.5 650 5.9 5.2 0.29 Comparative 2 ε iron oxide 3.2 4.5 8006.0 5.0 0.31 Comparative 3 BaFe 4 5.7 630 6.0 5.0 0.3 σ_(MD) V t_(m) S2t_(b) R_(ab) (N) (mm/min) (nm) (%) (μm) (nm) μ Example 1 0.75 0.5 90 650.6 5.2 0.53 Example 2 0.75 0.5 90 65 0.6 5.2 0.53 Example 3 0.75 0.5 9065 0.3 5.7 0.48 Example 4 0.75 0.5 90 65 0.3 5.7 0.48 Example 5 0.75 0.590 65 0.3 5.7 0.48 Example 6 0.75 0.5 90 65 0.3 5.7 0.48 Example 7 0.750.5 90 65 0.3 5.7 0.48 Example 8 0.75 0.5 90 65 0.3 5.7 0.48 Example 90.8 0.5 90 65 0.3 5.7 0.48 Example 10 3.5 0.5 90 65 0.3 5.7 0.48 Example11 0.8 5 90 65 0.3 5.7 0.48 Example 12 0.75 0.5 40 65 0.3 5.7 0.48Example 13 0.75 0.5 9 98 0.3 5.7 0.48 Example 14 0.75 0.5 90 65 0.2 5.70.48 Example 15 0.75 0.5 90 65 0.3 3.4 0.50 Example 16 0.75 0.5 90 650.3 5.7 0.20 Example 17 0.75 0.5 90 65 0.3 3.2 0.78 Example 18 0.75 0.5110 65 0.3 5.7 0.50 Example 19 0.75 0.5 90 65 0.3 7.2 0.50 Example 200.75 0.5 90 65 0.3 5.7 0.18 Example 21 0.75 0.5 90 65 0.3 5.7 0.82Example 22 0.75 0.5 90 73 0.3 5.7 0.48 Example 23 0.75 0.5 90 80 0.3 5.70.48 Example 24 5 0.5 90 65 0.3 5.7 0.48 Example 25 0.75 0.5 90 65 0.35.7 0.48 Example 26 0.75 0.5 90 65 0.3 5.7 0.50 Example 27 0.75 0.5 9065 0.6 5.7 0.50 Comparative 1 0.75 0.5 90 65 0.6 5.2 0.48 Comparative 20.75 0.5 90 65 0.3 5.7 0.50 Comparative 3 0.75 0.5 90 65 0.6 5.7 0.50Rating Rating Electromagnetic Rate of 1% (before (after conversionWinding shrinkage elongation storage) storage) characteristic deviation(%) load (N) Example 1 4 4 Good Good 0.05 0.59 Example 2 5 5 Good Good0.04 0.58 Example 3 6 5 Good Good 0.07 0.51 Example 4 7 6 Good Good 0.070.51 Example 5 7 6 Good Good 0.07 0.51 Example 6 8 7 Good Good 0.07 0.52Example 7 7 6 Good Good 0.07 0.51 Example 8 7 6 Good Good 0.07 0.51Example 9 8 7 Good Good 0.07 0.51 Example 10 8 7 Good Good 0.07 0.51Example 11 8 7 Good Good 0.07 0.51 Example 12 7 6 Good Good 0.07 0.51Example 13 7 6 Good Good 0.07 0.42 Example 14 7 6 Good Good 0.07 0.5 Example 15 7 6 Good Good 0.07 0.51 Example 16 7 6 Good Good 0.07 0.51Example 17 7 6 Good Good 0.07 0.51 Example 18 7 6 Bad Good 0.07 0.51Example 19 7 6 Good Good 0.07 0.51 Example 20 7 6 Good Bad 0.07 0.51Example 21 7 6 Good Bad 0.07 0.51 Example 22 8 7 Good Good 0.07 0.51Example 23 8 7 Fairly good Good 0.07 0.51 Example 24 8 7 Good Good 0.070.51 Example 25 7 6 Good Good 0.07 0.51 Example 26 4 4 Good Good 0.050.59 Example 27 4 4 Good Good 0.05 0.59 Comparative 1 4 1 Good Good 0.090.59 Comparative 2 6 1 Good Good 0.11 0.51 Comparative 3 2 1 Good Good0.07 0.63 Note that the symbols in Table 1 mean the followingmeasurement values. t_(T): thickness of magnetic tape (unit: μm) Δ_(W):dimensional variation of magnetic tape in the width direction to tensionchange of magnetic tape in the longitudinal direction (unit: ppm/N) α:thermal expansion coefficient of magnetic tape (unit: ppm/° C.) β:humidity expansion coefficient of magnetic tape (unit: ppm/% RH) ρ:Poisson's ratio of magnetic tape σ_(MD): elastic limit value of magnetictape in the longitudinal direction (unit: N) V: velocity in themeasurement of elastic limit (unit: mm/min) t_(m): average thickness ofmagnetic layer (unit: nm) S2: squareness ratio of magnetic tape in thethickness direction (vertical direction) (unit: %) t_(b): averagethickness of back layer (unit: μm) R_(ab): surface roughness of backlayer (unit: nm) μ: interlayer coefficient of friction between themagnetic surface and the back surface

The results given in Table 1 indicate the following.

For all of the magnetic tapes of Examples 1 to 27, the grade for thevariation of the tape width before and after storage was 4 or more (morespecifically, alienation from the ideal of “variation of effective tapewidth” was small. Therefore, the magnetic recording medium according tothe present technology is suitable to the use in a recording andreproducing apparatus which adjusts the tension in the longitudinaldirection.

Additionally, suitability to the recording and reproducing apparatus isalmost unchanged before and after storage. It is thus indicated thatsuitability to the recording and reproducing apparatus will be stablymaintained over a long period of time.

The grades for the tape width variation for Examples 1 to 27 indicatethat the dimensional variation Δw of the magnetic recording tape of 650ppm/N or more, more preferably 700 ppm/N or more, more preferably

750 ppm/N or more, and even more preferably 800 ppm/N or more makes themagnetic recording tape more suitable to the use in a recording andreproducing apparatus which adjusts the tension in the longitudinaldirection (particularly the adjustment of the tape width through theadjustment of the tension).

In comparison between Example 1 and Comparative Example 1, for themagnetic tape of Example 1, the rate of shrinkage in the longitudinaldirection was 0.05%, and the grade for the variation of the tape widthafter storage was 4, while for the magnetic tape of Comparative Example1, the rate of shrinkage in the longitudinal direction was 0.09%, andthe grade for the variation of the tape width after storage was 1.Additionally. in comparison between Example 7 and Comparative Example 2,for the magnetic tape of Example 7, the rate of shrinkage in thelongitudinal direction was 0.07%, and the grade for the variation of thetape width after storage was 6, while for the magnetic tape ofComparative Example 2, the rate of shrinkage in the longitudinaldirection was 0.11%, and the grade for the variation of the tape widthafter storage was 1. Therefore, the magnetic recording tape having arate of shrinkage of 0.08% or less, and preferably 0.07% or less in thelongitudinal direction suppresses deterioration of suitability to therecording and reproducing apparatus caused by storage.

Comparison of the evaluation results of Examples 3 to 6, and othersindicates that the thermal expansion coefficient α is preferably 5.9ppm/° C.≤α≤8 ppm/° C., from the viewpoint of suppressing alienation fromthe ideal “effective tape width variation”. In addition, Comparison ofthe evaluation results of Examples 3 to 6 indicates that the humidityexpansion coefficient β is preferably β≤5 ppm/% RH, from the viewpointof suppressing alienation from the ideal “effective tape widthvariation”.

Comparison of the evaluation results of Examples 7, 9, 10, and othersindicates that the elastic limit value σ_(MD) in the longitudinaldirection is preferably 0.8 N≤σ_(MD), from the viewpoint of suppressingalienation from the ideal “effective tape width variation”.

Comparison between Examples 9 and 11 indicates that the elastic limitvalue σ_(MD) does not depend on the velocity V in the measurement ofelastic limit.

Comparison of the evaluation results of Examples 7 and 18 indicates thatthe thickness of the magnetic layer is preferably 100 nm or less, andparticularly preferably 90 nm or less from the viewpoint of achievinggood electromagnetic conversion characteristic.

Comparison of the evaluation results of Examples 7, 15, 17, 19, andothers indicates that the surface roughness R_(ab) of the back layer ispreferably 3.2 nm≤R_(ab)≤7.2 nm from the viewpoint of achieving goodelectromagnetic conversion characteristic.

Mutual comparison of the evaluation results of Examples 7, 16, 17, 20,and 21 indicates that the coefficient of friction μ is preferably0.18<μ<0.82, particularly preferably 0.20≤μ≤0.80, more particularlypreferably 0.20≤μ≤0.78, and even more particularly preferably0.25≤μ≤0.75 from the viewpoint of suppressing winding deviation.

Comparison of the evaluation results of Examples 7, 22, and 23 indicatesthat the squareness ratio S2 of the magnetic tape is preferably 73% ormore, and particularly preferably 80% or more from the viewpoint ofachieving good electromagnetic conversion characteristic.

Comparison of the evaluation results of Examples 7, 25, 26, and othersindicates that the use of barium ferrite nanoparticles as magneticparticles achieves a similar evaluation result to that achieved by theuse of ε-iron oxide nanoparticles as magnetic particles.

Comparison of the results of Example 13 and other examples indicatesthat the magnetic recording tape of vacuum thin film type (sputteringtype) gives evaluation results similar to those of the magneticrecording tapes of coating type.

Embodiments and examples of the present technology are specificallydescribed above, but the present technology will not be limited to theabove embodiments and examples, and may be subjected to variousmodifications based on the technical thought of the present technology.

For example, the configurations, methods, processes, shapes, materials,and values given in the above-described embodiments and examples areonly exemplary, and other configurations, methods, processes, shapes,materials, and values different from the above-described ones may beused as necessary. Additionally, chemical formulae such as those ofcompounds are typical ones, and will not be limited to the valences andothers described herein as long as the general name of the same compoundis used.

Additionally, the configurations, methods, processes, shapes, materials,and values in the above-described embodiments and examples may becombined with each other without departing from the scope of the presenttechnology.

Additionally, in the present description, the value range indicatedusing “to” means the range including the values given before and after“to” as the minimum value and the maximum value, respectively. In thevalue range given in the present description stepwise, the upper limitor lower limit of a value range at one step may be replaced with theupper limit or lower limit of the value range at other step. Thematerials listed in the present description may be used alone or incombination of two or more, unless otherwise specified.

Note that the present technology may have the following configuration.

[1] A magnetic recording medium,

in which an average thickness t_(T) is t_(T)≤5.5 μm,

a dimensional variation Δw in a width direction to tension change in alongitudinal direction is 650 ppm/N≤Δw, and

a rate of shrinkage in the longitudinal direction is 0.08% or less.

[2] The magnetic recording medium according to [1], in which asquareness ratio in a vertical direction is 65% or more.

[3] The magnetic recording medium according to [1] or [2], in which thedimensional variation Δw is 700 ppm/N≤Δw.

[4] The magnetic recording medium according to [1] or [2], in which thedimensional variation Δw is 750 ppm/N≤Δw.

[5] The magnetic recording medium according to [1] or [2], in which thedimensional variation Δw is 800 ppm/N≤Δw.

[6] The magnetic recording medium according to any one of [1] to [5], inwhich the rate of shrinkage is 0.07% or less.

[7] The magnetic recording medium according to any one of [1] to [6],

in which the magnetic recording medium includes a back layer, and

a surface roughness R_(ab) of the back layer is 3.0 nm≤R_(ab)≤7.5 nm.

[8] The magnetic recording medium according to any one of [1] to [7],

in which the magnetic recording medium includes a magnetic layer and aback layer, and

a coefficient of friction μ between a surface on a side of the magneticlayer and a surface on a side of the back layer is 0.20≤μ≤0.80.

[9] The magnetic recording medium according to any one of [1] to [8], inwhich a 1% elongation load in the longitudinal direction is 0.60 N orless.

[10] The magnetic recording medium according to any one of [1] to [9],

in which a thermal expansion coefficient α is 5.5 ppm/° C.≤α≤9 ppm/° C.,and

a humidity expansion coefficient β is β≤5.5 ppm/% RH.

[11] The magnetic recording medium according to any one of [1] to [10],in which a Poisson's ratio ρ is 0.25≤ρ.

[12] The magnetic recording medium according to any one of [1] to [11],in which an elastic limit value σ_(MD) in the longitudinal direction is0.7 N≤σ_(MD).

[13] The magnetic recording medium according to [12], in which theelastic limit value σ_(MD) does not depend on a velocity V inmeasurement of elastic limit.

[14] The magnetic recording medium according to any one of [1] to [13],in which the magnetic recording medium includes a magnetic layer, andthe magnetic layer is vertically oriented.

[15] The magnetic recording medium according to any one of [1] to [14],in which the magnetic recording medium includes a back layer, and anaverage thickness t_(b) of the back layer is t_(b)≤0.6 μm.

[16] The magnetic recording medium according to any one of [1] to [15],in which the magnetic recording medium includes a magnetic layer, and

the magnetic layer is a sputtering layer.

[17] The magnetic recording medium according to [16], in which anaverage thickness t_(m) of the magnetic layer is 9 nm≤t_(m)≤90 nm.

[18] The magnetic recording medium according to any one of [1] to [15],

in which the magnetic recording medium includes a magnetic layer, and

the magnetic layer includes a magnetic powder.

[19] The magnetic recording medium according to [18], in which theaverage thickness t_(m) of the magnetic layer is 35 nm≤t_(m)≤120 nm.

[20] The magnetic recording medium according to [18] or [19], in whichthe magnetic powder includes an ε-iron oxide magnetic powder, a bariumferrite magnetic powder, a cobalt ferrite magnetic powder, or astrontium ferrite magnetic powder.

[21] The magnetic recording medium according to [2], in which the rateof shrinkage is 0.07% or less.

[22] The magnetic recording medium according to [2],

in which the magnetic recording medium includes a back layer, and

a surface roughness R_(ab) of the back layer is 3.0 nm≤R_(ab)≤7.5 nm.

[23] The magnetic recording medium according to [2],

in which the magnetic recording medium includes a magnetic layer and aback layer, and

a coefficient of friction μ between a surface on a side of the magneticlayer and a surface on a side of the back layer is 0.20≤μ≤0.80.

[24] The magnetic recording medium according to [2], in which a 1%elongation load in the longitudinal direction is 0.60 N or less.

[25] The magnetic recording medium according to [2], in which a thermalexpansion coefficient α is 5.5 ppm/° C.≤α≤9 ppm/° C., and, a humidityexpansion coefficient β is 5.5 ppm/% RH.

[26] The magnetic recording medium according to [2], in which aPoisson's ratio ρ is 0.25≤ρ.

[27] The magnetic recording medium according to [2], in which an elasticlimit value σ_(MD) in the longitudinal direction is 0.7 N≤σ_(MD).

[28] The magnetic recording medium according to [27], in which theelastic limit value σ_(MD) does not depend on a velocity V inmeasurement of elastic limit.

REFERENCE SIGNS LIST

-   10 Magnetic recording medium-   11 Base layer-   12 Primary layer-   13 Magnetic layer-   14 Back layer

The invention claimed is:
 1. A magnetic recording medium comprising amagnetic layer, a non-magnetic layer, a base layer and a back layer,wherein an average thickness t_(T) of the magnetic recording medium ist_(T)≤5.3 μm, a dimensional variation Δw in a width direction of themagnetic recording medium to tension change in a longitudinal directionof the magnetic recording medium is 700 ppm/N≤Δw, a rate of shrinkage inthe longitudinal direction of the magnetic recording medium is 0.08% orless, and wherein the dimensional variation Δw is determined accordingto:${\Delta\;{w\lbrack {{ppm}\text{/}N} \rbrack}} = {\frac{{{D( {0.2N} )}\lbrack{mm}\rbrack} - {{D( {1.0N} )}\lbrack{mm}\rbrack}}{{D( {0.2N} )}\lbrack{mm}\rbrack} \times \frac{1\text{,}000\text{,}000}{( {1.0\lbrack N\rbrack} ) - ( {0.2\lbrack N\rbrack} )}}$where D(0.2 N) and D(1.0 N) represent widths of a sample of the magneticrecording medium subject to loads of 0.2 N and 1.0 N, respectively, inthe longitudinal direction of the magnetic recording medium and a widthof the sample of the magnetic recording medium is ½ inch prior to beingsubject to a load.
 2. The magnetic recording medium according to claim1, wherein a squareness ratio in a vertical direction of the magneticrecording medium is 65% or more.
 3. The magnetic recording mediumaccording to claim 1, wherein the dimensional variation Δw is 750ppm/N≤Δw.
 4. The magnetic recording medium according to claim 1, whereinthe dimensional variation Δw is 800 ppm/N≤Δw.
 5. The magnetic recordingmedium according to claim 1, wherein the rate of shrinkage in thelongitudinal direction is 0.07% or less.
 6. The magnetic recordingmedium according to claim 1, wherein a surface roughness R_(ab) of theback layer is 3.0 nm≤R_(ab)≤7.5 nm.
 7. The magnetic recording mediumaccording to claim 1, wherein a coefficient of friction μ between asurface on a side of the magnetic layer and a surface on a side of theback layer is 0.20≤μ≤0.80.
 8. The magnetic recording medium according toclaim 1, wherein a 1% elongation load in the longitudinal direction is0.60 N or less, and wherein the 1% elongation load is determined bypulling a sample of the magnetic recording medium at 10 mm/mm under a0.6% elongation load and a 1.5% elongation load.
 9. The magneticrecording medium according to claim 1, wherein a thermal expansioncoefficient α is 5.5 ppm/° C.≤α≤9 ppm/° C., and a humidity expansioncoefficient β is β≤5.5 ppm/% RH.
 10. The magnetic recording mediumaccording to claim 1, wherein a Poisson's ratio ρ is 0.25≤ρ.
 11. Themagnetic recording medium according to claim 1, wherein an elastic limitvalue a MD in the longitudinal direction is 0.7 N≤σ_(MB) and wherein theelastic limit value σ_(MD) is determined by pulling a sample of themagnetic recording medium at 0.5 mm/mm to obtain a distance versus loadrelationship.
 12. The magnetic recording medium according to claim 11,wherein the elastic limit value σ_(MB) does not depend on a velocity Vin measurement of elastic limit.
 13. The magnetic recording mediumaccording to claim 1, wherein the magnetic layer is vertically oriented.14. The magnetic recording medium according to claim 1, wherein anaverage thickness t_(b) of the back layer is t_(b)≤0.6 μm.
 15. Themagnetic recording medium according to claim 1, wherein the magneticlayer includes a magnetic powder.
 16. The magnetic recording mediumaccording to claim 15, wherein the average thickness t_(m) of themagnetic layer is 35 nm≤t_(m)≤120 nm.
 17. The magnetic recording mediumaccording to claim 15, wherein the magnetic powder includes an ε-ironoxide magnetic powder, a barium ferrite magnetic powder, a cobaltferrite magnetic powder, or a strontium ferrite magnetic powder.
 18. Themagnetic recording medium according to claim 1, wherein a squarenessratio in a vertical direction of the magnetic recording medium is 73% ormore.
 19. The magnetic recording medium according to claim 1, whereinthe average thickness t_(T) of the magnetic recording medium ist_(T)≤5.2 μm.
 20. The magnetic recording medium according to claim 1,wherein a squareness ratio in a vertical direction of the magneticrecording medium is 65% or more, the magnetic layer includes a bariumferrite magnetic powder, the average thickness t_(m) of the magneticlayer is 35 nm≤t_(m)≤100 nm, a coercivity Hc in the vertical directionof the magnetic recording medium is 160 kA/m or more and 280 kA/m orless, the base layer includes a polyester resin, and the magneticrecording medium includes three to ten servo bands on the magneticlayer.